Power output apparatus, method of controlling power output apparatus, and driving system with power output apparatus incorporated therein

ABSTRACT

A power output apparatus 20 includes a clutch motor, an assist motor, and a controller. The clutch motor and the assist motor are controlled by the controller to enable the power output from an engine to a crankshaft 56, and expressed as the product of its revolving speed and torque, to be converted to the power expressed as the product of a revolving speed and a torque of a drive shaft and to be output to the drive shaft. The engine can be driven at an arbitrary driving point defined by a revolving speed and a torque, as long as the energy or power output to the crankshaft is identical. A desired driving point that attains the highest possible efficiency with respect to each amount of output energy is determined in advance. In order to allow the engine to be driven at the desired driving point, the controller controls the clutch motor and the assist motor as well as the fuel injection and the throttle valve position. Such control procedures of the power output apparatus enhance the energy efficiency of the whole power output apparatus.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power output apparatus, a method ofcontrolling a power output apparatus, and a driving system with a poweroutput apparatus incorporated therein. More concretely, the presentinvention pertains to a power output apparatus for outputting powergenerated by an engine to a drive shaft at a high efficiency and amethod of controlling such a power output apparatus, as well as adriving system with such a power output apparatus incorporated therein.

2. Description of Related Art

In known power output apparatuses mounted on a vehicle, an output shaftof an engine is electromagnetically linked with a drive shaft, whichconnects with a rotor of a motor, by means of an electromagneticcoupling, so that power of the engine is transmitted to the drive shaft(as disclosed in, for example, JAPANESE PATENT LAYING-OPEN GAZETTE No.53-133814). The electromagnetic coupling of the power output apparatustransmits part of the power output from the engine as a torque to thedrive shaft via electromagnetic connection, and supplies electric powerregenerated by sliding motions of the electromagnetic coupling to themotor and secondary cells, which are connected in parallel with theelectromagnetic coupling. When the torque transmitted to the drive shaftby means of the electromagnetic coupling is insufficient, the motorapplies an additional torque to the drive shaft with the electric powerregenerated by the electromagnetic coupling or the electric powerreleased from the secondary cells. The motor works as a generator when abraking force is applied to the drive shaft, so as to regenerate theenergy of rotational motion of the drive shaft as electrical energy andstore the regenerated electrical energy in the secondary cells.

In the conventional power output apparatuses, however, problems, such asan extremely low energy efficiency of the whole apparatus or anextremely poor emission, arise in some cases. The power output apparatuscan implement torque conversion of all the power output from the enginewith the electromagnetic coupling and the motor and output the convertedpower to the drive shaft. The electromagnetic coupling and the motorcarry out energy conversion of the power or energy expressed as theproduct of the torque and the revolving speed of the engine into thepower or energy expressed as the product of the torque and the revolvingspeed of the drive shaft under the condition of constant energy. on theassumption that the conversion efficiency is an ideal state (that is,the value `1`), the object of torque conversion is to make the poweroutput from the engine equal to the power output to the drive shaft. Theengine may accordingly be driven at any driving point (defined by therevolving speed and the torque) that can output energy identical withthe power. Without the active control of the driving point of theengine, this often causes the engine to be driven at driving points oflow energy efficiency or poor emission.

SUMMARY OF THE INVENTION

One object of the present invention is thus to provide a power outputapparatus and a method of controlling the same that enhance the energyefficiency of the whole power output apparatus.

Another object of the present invention is to provide a power outputapparatus and a method of controlling the same that improve theemission.

Still another object is to provide a power output apparatus and a methodof controlling the same that enable the engine to be smoothly shifted toa new driving point with a variation in power to be output to the driveshaft.

Further object is to provide a driving system that prevents the drivingsystem itself or a power output apparatus or any other equipmentincorporated in the driving system from resonating due to an operationof the engine in the power output apparatus.

At least part of the above objects is realized by a first power outputapparatus for outputting power to a drive shaft. The first power outputapparatus includes: an engine having an output shaft; energy adjustmentmeans having a first shaft connected with the output shaft of the engineand a second shaft connected with the drive shaft, the energy adjustmentmeans adjusting a difference in energy between power input into oroutput from the first shaft and power input into or output from thesecond shaft by regulating input and output of corresponding electricalenergy; a drive motor, wherein power is transmitted between the drivemotor and the drive shaft; target power setting means for setting atarget power output to the drive shaft; driving state setting means forsetting a target driving state of the engine that outputs energycorresponding to the target power set by the target power setting means,based on a predetermined condition; and control means for controllingthe engine, so as to enable the engine to be driven in the targetdriving state set by the driving state setting means, and forcontrolling the energy adjustment means and the drive motor, so as toenable power output from the engine to be subjected to torque conversionand output as the target power to the drive shaft.

The first power output apparatus of the invention enables the engine tobe driven in the target driving state that has been set based on thepredetermined condition, among the available driving states which canoutput energy corresponding to the target power.

In the first power output apparatus, the predetermined condition usedfor setting the target driving state may be a condition for enhancing anenergy efficiency of the engine that outputs energy corresponding to thetarget power. This condition enhances the energy efficiency of theengine. The predetermined condition may also be a condition forenhancing a comprehensive efficiency, which is calculated by multiplyingan energy efficiency of the engine that outputs energy corresponding tothe target power by a transmission efficiency of the energy adjustmentmeans and the drive motor when the power output from the engine issubjected to torque conversion and output to the drive shaft. Thiscondition enhances the efficiency of the whole power output apparatus.The predetermined condition may otherwise be a condition forcontinuously varying a driving state of the engine with a variation intarget power. This condition allows the engine to smoothly shift itsdriving state with a variation in target power.

In accordance with one aspect of the present invention, the energyadjustment means of the first power output apparatus may be constructedas a twin-rotor motor comprising a first rotor connected with the firstshaft and a second rotor connected with the second shaft, the secondrotor being rotatable relative to the first rotor, whereby power istransmitted between the first shaft and the second shaft via anelectromagnetic coupling of the first rotor with the second rotor, thetwin-rotor motor inputting and outputting electrical energy based on theelectromagnetic coupling of the first rotor with the second rotor and adifference in revolving speed between the first rotor and the secondrotor.

In the first power output apparatus including the twin-rotor motor asthe energy adjustment means, the drive motor may include the secondrotor included in the twin-rotor motor and a stator for rotating thesecond rotor. This effectively reduces the size of the whole poweroutput apparatus.

In accordance with another aspect of the present invention, the energyadjustment means of the first power output apparatus may be constructedas: three-shaft-type power input and output means connected with thefirst shaft, the second shaft, and a third shaft, the three-shaft-typepower input and output means for, when powers input into or output fromany two shafts among the three different shafts are determined,automatically setting a power input into or output from a residual shaftbased on the powers thus determined; and a shaft motor connected withthe third shaft, wherein power is transmitted between the third shaftand the shaft motor.

In accordance with another aspect of the present invention, the firstpower output apparatus further includes driving state detecting meansfor detecting a driving state of the engine. The control means furtherhas means for controlling the energy adjustment means, so as to enablethe engine to be driven in the target driving state, based on thedriving state of the engine detected by the driving state detectingmeans. This structure ensures the operation of the engine in the targetdriving state.

In accordance with another aspect of the present invention, the firstpower output apparatus further includes driving state detecting meansfor detecting a driving state of the engine. The control means furtherhas tentative target driving state setting means for, when a statedeviation of the driving state detected by the driving state detectingmeans from the target driving state is out of a predetermined range,selecting a driving state within the predetermined range based on thestate deviation and the predetermined condition and setting the selecteddriving state as a tentative target driving state. The tentative targetdriving state set by the tentative target driving state setting means isused in place of the target driving state for operation control of theengine and control of the energy adjustment means and the drive motor,until the state deviation enters the predetermined range. Even when thenewly set target driving state has a large state deviation, thisstructure enables the engine to stably approach to and eventually reachthe target driving state. This effectively prevents the engine fromstalling or stopping the revolutions of its output shaft due to thelarge state deviation.

In the first power output apparatus wherein the control means has thetentative target driving state setting means, it is preferable that thetentative target driving state setting means further includespredetermined range setting means for setting the predetermined rangebased on the driving state detected by the driving state detectingmeans. This structure enables the requirement or non-requirement forsetting the tentative target driving state to be determined according tothe driving state of the engine.

In the first power output apparatus wherein the control means has thetentative target driving state setting means, the control means mayfurther include means for controlling the energy adjustment means, so asto enable the engine to be driven in the target driving state, based onthe driving state detected by the driving state detecting means, whenthe state deviation is within the predetermined range. This structurefurther ensures the operation of the engine in the target driving statewhen the state deviation is within the predetermined range.

In accordance with one aspect of the present invention, the first poweroutput apparatus, wherein the control means has the tentative targetdriving state setting means, further includes storage battery meansbeing charged with electrical energy taken out of the energy adjustmentmeans, being charged with electrical energy taken out of the drivemotor, being discharged to release electrical energy used in the energyadjustment means, and being discharged to release electrical energy usedin the drive motor. The control means further has means for, when thetentative target driving state is used in place of the target drivingstate for the operation control of the engine and the control of theenergy adjustment means and the drive motor, utilizing the electricalenergy stored into or released from the storage battery means andcontrolling the drive motor, so as to enable the drive motor to input oroutput a specific power into or from the drive shaft, the specific powercorresponding to an energy difference between the target power and thepower output from the engine that is driven in the tentative targetdriving state. This structure enables the target power to be output tothe drive shaft even, when there is a large difference between theactual driving state of the engine and the target driving state.

In the first power output apparatus, it is also preferable that thecontrol means further includes: driving state estimating means forestimating a driving state of the engine when the target power settingmeans sets a different target power; and estimated-condition controlmeans for controlling the energy adjustment means and the drive motorbased on the estimated driving state of the engine. This structureenables the engine to smoothly shift to the target driving state. With avariation in target power, the first power output apparatus constructedas above can effectively implement torque conversion of the power outputfrom the engine and output the converted power to the drive shaft with ahigh efficiency.

In the first power output apparatus wherein the control means has thedriving state estimating means and the estimated-condition controlmeans, it is further preferable that the driving state estimating meansincludes means for estimating the driving state of the engine based on arevolving speed of the output shaft of the engine and a state of theenergy adjustment means.

In the first power output apparatus wherein the control means has thedriving state estimating means and the estimated-condition controlmeans, it is also preferable that the estimated-condition control meansfurther has means for controlling the energy adjustment means and thedrive motor, so as to enable an estimated power output from the enginecorresponding to the driving state of the engine estimated by thedriving state estimating means to be subjected to torque conversion andoutput as the target power to the drive shaft. This structure enablesthe power output from the engine to be subjected to torque conversionand to be output to the drive shaft, even in the transient period ofvaried target power.

In accordance with another aspect of the present invention, the firstpower output apparatus, wherein the control means has the driving stateestimating means and the estimated-condition control means, furtherincludes storage battery means being charged with electrical energytaken out of the energy adjustment means, being charged with electricalenergy taken out of the drive motor, being discharged to releaseelectrical energy used in the energy adjustment means, and beingdischarged to release electrical energy used in the drive motor. Theestimated-condition control means has means for utilizing the electricalenergy stored into or released from the storage battery means andcontrolling the drive motor, so as to enable the drive motor to input oroutput a specific power into or from the drive shaft, the specific powercorresponding to an energy difference between the target power and theestimated power output from the engine corresponding to the drivingstate of the engine estimated by the driving state estimating means.Even when the engine is not driven in the target driving state in thetransient period of varied target power, the target power can be therebyoutput to the drive shaft.

The present invention is also directed to a second power outputapparatus for outputting power to a drive shaft. The second power outputapparatus includes: an engine having an output shaft; energy adjustmentmeans having a first shaft connected with the output shaft of the engineand a second shaft connected with the drive shaft, the energy adjustmentmeans adjusting a difference in energy between power input into oroutput from the first shaft and power input into or output from thesecond shaft by regulating input and output of corresponding electricalenergy; a drive motor, wherein power is transmitted between the drivemotor and the output shaft of the engine; target power setting means forsetting a target power output to the drive shaft; driving state settingmeans for setting a target driving state of the engine that outputsenergy corresponding to the target power set by the target power settingmeans, based on a predetermined condition; and control means forcontrolling the engine, so as to enable the engine to be driven in thetarget driving state set by the driving state setting means, and forcontrolling the energy adjustment means and the drive motor, so as toenable power output from the engine to be subjected to torque conversionand output as the target power to the drive shaft.

The second power output apparatus of the invention enables the engine tobe driven in the target driving state that has been set based on thepredetermined condition, among the available driving states which canoutput energy corresponding to the target power.

In the second power output apparatus, the predetermined condition usedfor setting the target driving state may be a condition for enhancing anenergy efficiency of the engine that outputs energy corresponding to thetarget power. This condition enhances the energy efficiency of theengine. The predetermined condition may also be a condition forenhancing a comprehensive efficiency, which is calculated by multiplyingan energy efficiency of the engine that outputs energy corresponding tothe target power by a transmission efficiency of the energy adjustmentmeans and the drive motor when the power output from the engine issubjected to torque conversion and output to the drive shaft. Thiscondition enhances the efficiency of the whole power output apparatus.The predetermined condition may otherwise be a condition forcontinuously varying a driving state of the engine with a variation intarget power. This condition allows the engine to smoothly shift itsdriving state with a variation in target power.

In accordance with one aspect of the present invention, the energyadjustment means of the second power output apparatus may be constructedas a twin-rotor motor comprising a first rotor connected with the firstshaft and a second rotor connected with the second shaft, the secondrotor being rotatable relative to the first rotor, whereby power istransmitted between the first shaft and the second shaft via anelectromagnetic coupling of the first rotor with the second rotor, thetwin-rotor motor inputting and outputting electrical energy based on theelectromagnetic coupling of the first rotor with the second rotor and adifference in revolving speed between the first rotor and the secondrotor.

In the second power output apparatus including the twin-rotor motor asthe energy adjustment means, the drive motor may include the first rotorincluded in the twin-rotor motor and a stator for rotating the firstrotor. This effectively reduces the size of the whole power outputapparatus.

In accordance with another aspect of the present invention, the energyadjustment means of the second power output apparatus may be constructedas: three-shaft-type power input and output means connected with thefirst shaft, the second shaft, and a third shaft, the three-shaft-typepower input and output means for, when powers input into or output fromany two shafts among the three different shafts are determined,automatically setting a power input into or output from a residual shaftbased on the powers thus determined; and a shaft motor connected withthe third shaft, wherein power is transmitted between the third shaftand the shaft motor.

In accordance with another aspect of the present invention, the secondpower output apparatus further includes driving state detecting meansfor detecting a driving state of the engine. The control means furtherhas tentative target driving state setting means for, when a statedeviation of the driving state detected by the driving state detectingmeans from the target driving state is out of a predetermined range,selecting a driving state within the predetermined range based on thestate deviation and the predetermined condition and setting the selecteddriving state as a tentative target driving state. The tentative targetdriving state set by the tentative target driving state setting means isused in place of the target driving state for operation control of theengine and control of the energy adjustment means and the drive motor,until the state deviation enters the predetermined range. Even when thenewly set target driving state has a large state deviation, thisstructure enables the engine to stably approach to and eventually reachthe target driving state. This effectively prevents the engine fromstalling or stopping the revolutions of its output shaft due to thelarge state deviation.

In the second power output apparatus, it is also preferable that thecontrol means further includes: driving state estimating means forestimating a driving state of the engine when the target power settingmeans sets a different target power; and estimated-condition controlmeans for controlling the energy adjustment means and the drive motorbased on the estimated driving state of the engine. This structureenables the engine to smoothly shift to the target driving states With avariation in target power, the first power output apparatus constructedas above can effectively implement torque conversion of the power outputfrom the engine and output the converted power to the drive shaft with ahigh efficiency.

In the second power output apparatus wherein the control means has thedriving state estimating means and the estimated-condition controlmeans, it is also preferable that the estimated-condition control meansfurther has means for controlling the energy adjustment means and thedrive motor, so as to enable an estimated power output from the enginecorresponding to the driving state of the engine estimated by thedriving state estimating means to be subjected to torque conversion andoutput as the target power to the drive shaft. This structure enablesthe power output from the engine to be subjected to torque conversionand to be output to the drive shaft, even in the transient period ofvaried target power.

In accordance with another aspect of the present invention, the secondpower output apparatus, wherein the control means has the driving stateestimating means and the estimated-condition control means, furtherincludes storage battery means being charged with electrical energytaken out of the energy adjustment means, being charged with electricalenergy taken out of the drive motor, being discharged to releaseelectrical energy used in the energy adjustment means, and beingdischarged to release electrical energy used in the drive motor. Theestimated-condition control means has means for utilizing the electricalenergy stored into or released from the storage battery means andcontrolling the drive motor, so as to enable the drive motor to input oroutput a specific power into or from the output shaft of the engine, thespecific power corresponding to an energy difference between the targetpower and the estimated power output from the engine corresponding tothe driving state of the engine estimated by the driving stateestimating means. Even when the engine is not driven in the targetdriving state in the transient period of varied target power, the targetpower can be thereby output to the drive shaft.

The present invention is further directed to a first driving system,which includes: an engine having an output shaft; energy adjustmentmeans having a first shaft connected with the output shaft of the engineand a second shaft connected with a drive shaft of the driving system,the energy adjustment means adjusting a difference in energy betweenpower input into or output from the first shaft and power input into oroutput from the second shaft by regulating input and output ofcorresponding electrical energy; a drive motor, wherein power istransmitted between the drive motor and the drive shaft; target powersetting means for setting a target power output to the drive shaft;driving state setting means for setting a target driving state of theengine that outputs energy corresponding to the target power set by thetarget power setting means, based on a first condition for enhancing anenergy efficiency of the engine that outputs energy corresponding to thetarget power and a second condition for making a vibration due to anoperation of the engine out of a range of resonance frequency of thedriving system; and control means for controlling the engine, so as toenable the engine to be driven in the target driving state set by thedriving state setting means, and for controlling the energy adjustmentmeans and the drive motor, so as to enable power output from the engineto be subjected to torque conversion and output as the target power tothe drive shaft.

Typical examples of the first driving system of the present inventioninclude vehicles, ships, airplanes, and various industrial machines. Thefirst driving system can effectively prevent the driving system itselfor a power output apparatus or any other equipment incorporated in thedriving system from resonating due to an operation of the engine. Noundesirable stress due to the resonance is thereby applied to thedriving system or other equipment incorporated in the driving system, sothat the driving system and the other equipment have better durabilityand the engine can be driven at driving points of the highest possibleefficiency. This improves the energy efficiency of the whole system.

In accordance with one aspect of the present invention, the energyadjustment means of the first driving system may be constructed as atwin-rotor motor comprising a first rotor connected with the first shaftand a second rotor connected with the second shaft, the second rotorbeing rotatable relative to the first rotor, whereby power istransmitted between the first shaft and the second shaft via anelectromagnetic coupling of the first rotor with the second rotor, thetwin-rotor motor inputting and outputting electrical energy based on theelectromagnetic coupling of the first rotor with the second rotor and adifference in revolving speed between the first rotor and the secondrotor.

In the first driving system including the twin-rotor motor as the energyadjustment means, the drive motor may include the second rotor includedin the twin-rotor motor and a stator for rotating the second rotor. Thiseffectively reduces the size of the whole power output apparatus.

In accordance with another aspect of the present invention, the energyadjustment means of the first driving system may be constructed as:three-shaft-type power input and output means connected with the firstshaft, the second shaft, and a third shaft, the three-shaft-type powerinput and output means for, when powers input into or output from anytwo shafts among the three different shafts are determined,automatically setting a power input into or output from a residual shaftbased on the powers thus determined; and a shaft motor connected withthe third shaft, wherein power is transmitted between the third shaftand the shaft motor.

The present invention is further directed to a second driving system,which includes: an engine having an output shaft; energy adjustmentmeans having a first shaft connected with the output shaft of the engineand a second shaft connected with a drive shaft of the driving system,the energy adjustment means adjusting a difference in energy betweenpower input into or output from the first shaft and power input into oroutput from the second shaft by regulating input and output ofcorresponding electrical energy; a drive motor, wherein power istransmitted between the drive motor and the output shaft of the engine;target power setting means for setting a target power output to thedrive shaft; driving state setting means for setting a target drivingstate of the engine that outputs energy corresponding to the targetpower set by the target power setting means, based on a first conditionfor enhancing an energy efficiency of the engine that outputs energycorresponding to the target power and a second condition for making avibration due to an operation of the engine out of a range of resonancefrequency of the driving system; and control means for controlling theengine, so as to enable the engine to be driven in the target drivingstate set by the driving state setting means, and for controlling theenergy adjustment means and the drive motor, so as to enable poweroutput from the engine to be subjected to torque conversion and outputas the target power to the drive shaft.

Typical examples of the second driving system of the present inventioninclude vehicles, ships, airplanes, and various industrial machines. Thesecond driving system can effectively prevent the driving system itselfor a power output apparatus or any other equipment incorporated in thedriving system from resonating due to an operation of the engine. Noundesirable stress due to the resonance is thereby applied to thedriving system or other equipment incorporated in the driving system, sothat the driving system and the other equipment have better durabilityand the engine can be driven at driving points of the highest possibleefficiency. This improves the energy efficiency of the whole system.

In accordance with one aspect of the present invention, the energyadjustment means of the second driving system may be constructed as atwin-rotor motor comprising a first rotor connected with the first shaftand a second rotor connected with the second shaft, the second rotorbeing rotatable relative to the first rotor, whereby power istransmitted between the first shaft and the second shaft via anelectromagnetic coupling of the first rotor with the second rotor, thetwin-rotor motor inputting and outputting electrical energy based on theelectromagnetic coupling of the first rotor with the second rotor and adifference in revolving speed between the first rotor and the secondrotor.

In the second driving system including the twin-rotor motor as theenergy adjustment means, the drive motor may include the first rotorincluded in the twin-rotor motor and a stator for rotating the firstrotor. This effectively reduces the size of the whole power outputapparatus.

In accordance with another aspect of the present invention, the energyadjustment means of the second driving system may be constructed as:three-shaft-type power input and output means connected with the firstshaft the second shaft, and a third shaft, the three-shaft-type powerinput and output means for, when powers input into or output from anytwo shafts among the three different shafts are determined,automatically setting a power input into or output from a residual shaftbased on the powers thus determined; and a shaft motor connected withthe third shaft, wherein power is transmitted between the third shaftand the shaft motor.

At least part of the above objects is also realized by a first method ofcontrolling a power output apparatus for outputting power to a driveshaft. The first method includes the steps of: (a) providing an enginehaving an output shaft; energy adjustment means having a first shaftconnected with the output shaft of the engine and a second shaftconnected with the drive shaft, the energy adjustment means adjusting adifference in energy between power input into or output from the firstshaft and power input into or output from the second shaft by regulatinginput and output of corresponding electrical energy; and a drive motor,wherein power is transmitted between the drive motor and the driveshaft; (b) setting a target power output to the drive shaft; (c) settinga target driving state of the engine that outputs energy correspondingto the target power set in the step (b), based on a specific conditionof selecting a specific driving point that attains a highest possibleefficiency among a plurality of available driving points of the enginethat outputs energy corresponding to the target power; and (d)controlling the engine, so as to enable the engine to be driven in thetarget driving state set in the step (c), and for controlling the energyadjustment means and the drive motor, so as to enable power output fromthe engine to be subjected to torque conversion and output as the targetpower to the drive shaft.

The first method of the present invention enables the engine to bedriven in a specific driving point that attains the highest possibleefficiency among a plurality of available driving points of the enginethat outputs energy corresponding to the target power. This furtherenhances the energy efficiency of the power output apparatus.

In the first method of the present invention, the step (d) may furtherinclude the steps of: (e) detecting a driving state of the engine; (f)when a state deviation of the driving state of the engine detected inthe step (e) from the target driving state is out of a predeterminedrange, selecting a driving state within the predetermined range based onthe state deviation and the specific condition and setting the selecteddriving state as a tentative target driving state; and (g) using thetentative target driving state set in the step (f) in place of thetarget driving state, in order to control the engine, the energyadjustment means, and the drive motor, until the state deviation entersthe predetermined range. Even when the newly set target driving statehas a large state deviation, this structure enables the engine to stablyapproach to and eventually reach the target driving state. Thiseffectively prevents the engine from stalling or stopping therevolutions of its output shaft due to the large state deviation.

In the first method of the present invention, it is also desirable thatthe step (d) further includes the steps of: (h) when a different targetpower is set, estimating a driving state of the engine based on arevolving speed of the output shaft of the engine and a state of theenergy adjustment means; and (i) controlling the energy adjustment meansand the drive motor, so as to enable power output from the engine to besubjected to torque conversion and output to the drive shaft, based onthe estimated driving state of the engine. With a variation in targetpower, this structure enables the power output from the engine to besubjected to torque conversion and to be output to the drive shaft witha high efficiency.

The present invention is further directed to a second method ofcontrolling a power output apparatus for outputting power to a driveshaft. The second method includes the steps of: (a) providing an enginehaving an output shaft; energy adjustment means having a first shaftconnected with the output shaft of the engine and a second shaftconnected with the drive shaft, the energy adjustment means adjusting adifference in energy between power input into or output from the firstshaft and power input into or output from the second shaft by regulatinginput and output of corresponding electrical energy; and a drive motor,wherein power is transmitted between the drive motor and the driveshaft; (b) setting a target power output to the drive shaft; (c) settinga target driving state of the engine that outputs energy correspondingto the target power set in the step (b), based on a specific conditionof selecting a specific driving point that attains a highest possiblecomprehensive efficiency among a plurality of available driving pointsof the engine that outputs energy corresponding to the target power, thecomprehensive efficiency being calculated by multiplying an energyefficiency of the engine by a transmission efficiency of the energyadjustment means and the drive motor when the power output from theengine is subjected to torque conversion and output to the drive shaft;and (d) controlling the engine, so as to enable the engine to be drivenin the target driving state set in the step (c), and for controlling theenergy adjustment means and the drive motor, so as to enable poweroutput from the engine to be subjected to torque conversion and outputas the target power to the drive shaft.

The second method of the present invention enables the engine to bedriven in a specific driving point that attains the highest possiblecomprehensive efficiency of the whole apparatus, among a plurality ofavailable driving points of the engine that outputs energy correspondingto the target power. This further enhances the energy efficiency of thepower output apparatus.

In the second method of the present invention, the step (d) may furtherinclude the steps of: (e) detecting a driving state of the engine; (f)when a state deviation of the driving state of the engine detected inthe step (e) from the target driving state is out of a predeterminedrange, selecting a driving state within the predetermined range based onthe state deviation and the specific condition and setting the selecteddriving state as a tentative target driving state; and (g) using thetentative target driving state set in the step (f) in place of thetarget driving state, in order to control the engine, the energyadjustment means, and the drive motor, until the state deviation entersthe predetermined range. Even when the newly set target driving statehas a large state deviation, this structure enables the engine to stablyapproach to and eventually reach the target driving state. Thiseffectively prevents the engine from stalling or stopping therevolutions of its output shaft due to the large state deviation.

In the second method of the present invention, it is also desirable thatthe step (d) further includes the steps of: (h) when a different targetpower is set, estimating a driving state of the engine based on arevolving speed of the output shaft of the engine and a state of theenergy adjustment means; and (i) controlling the energy adjustment meansand the drive motor, so as to enable power output from the engine to besubjected to torque conversion and output to the drive shaft, based onthe estimated driving state of the engine. With a variation in targetpower, this structure enables the power output from the engine to besubjected to torque conversion and to be output to the drive shaft witha high efficiency.

These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiments with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating structure of a power outputapparatus as a first embodiment according to the present invention;

FIG. 2 is a cross sectional view illustrating detailed structures of aclutch motor and an assist motor included in the power output apparatusof FIG. 1;

FIG. 3 is a schematic view illustrating general structure of a vehiclewith the power output apparatus of FIG. 1 incorporated therein;

FIG. 4 is a graph showing the operation principle of the power outputapparatus;

FIG. 5 is a flowchart showing a torque control routine executed in thefirst embodiment by the control CPU of the controller;

FIG. 6 is a graph illustrating driving points of the engine defined bythe target engine torque and the target revolving speed;

FIG. 7 is a graph showing the efficiency of the engine along theconstant-output energy curves against the revolving speed of the engine;

FIG. 8 is a flowchart showing a fundamental procedure of controlling theclutch motor executed by the controller;

FIG. 9 is a graph showing the relationship between the torque commandvalue of the clutch motor and the target torque and the target revolvingspeed of the engine;

FIGS. 10 and 11 are flowcharts showing a fundamental procedure ofcontrolling the assist motor executed by the controller 80;

FIG. 12 is a flowchart showing a throttle valve position control routineexecuted by the electronic control unit;

FIG. 13 is a flowchart showing a fuel injection control routine executedby the electronic control unit;

FIG. 14 is a graph showing driving points of the engine by taking intoaccount a resonant revolving speed range of the vehicle or equipmentmounted on the vehicle;

FIG. 15 is an enlarged view showing the resonant revolving speed rangeof FIG. 14 and its vicinity;

FIG. 16 is a flowchart showing a torque control routine executed in asecond embodiment of the present invention by the control CPU of thecontroller;

FIG. 17 shows variations in accelerator pedal position, output energy,and torque when the driver steps on the accelerator pedal;

FIG. 18 is a flowchart showing a control procedure of the assist motorexecuted by the controller in a modification of the second embodiment;

FIGS. 19 and 20 are flowcharts showing a control procedure of the clutchmotor executed in a third embodiment of the present invention by thecontroller;

FIG. 21 shows a process of leading the estimated target revolving speedfrom the estimated torque;

FIG. 22 shows variations in accelerator pedal position, throttle valveposition, and torque and revolving speed of the engine when the driversteps on the accelerator pedal;

FIG. 23 shows structure of another power output apparatus as amodification of the first through the third embodiments;

FIG. 24 shows structure of still another power output apparatus as afourth embodiment of the present invention;

FIG. 25 shows structure of another power output apparatus as amodification of the fourth embodiment;

FIG. 26 shows structure of still another power output apparatus asanother modification of the fourth embodiment;

FIG. 27 shows structure of another power output apparatus as a fifthembodiment according to the present invention;

FIG. 28 is an enlarged view illustrating an essential part of the poweroutput apparatus of the fifth embodiment;

FIG. 29 is a schematic view illustrating general structure of a vehiclewith the power output apparatus of the fifth embodiment incorporatedtherein;

FIG. 30 is a nomogram showing the relationship between the revolvingspeed and the torque of the three different shafts linked with theplanetary gear;

FIG. 31 is a nomogram showing the relationship between the revolvingspeed and the torque of the three different shafts linked with theplanetary gear;

FIG. 32 is a flowchart showing a torque control routine executed in thefifth embodiment by the control CPU of the controller;

FIGS. 33 and 34 are flowcharts showing a control procedure of the firstmotor MG1 executed in the fifth embodiment by the controller;

FIG. 35 is a flowchart showing a control procedure of the second motorexecuted in the fifth embodiment by the controller;

FIG. 36 shows structure of another power output apparatus as amodification of the fifth embodiment;

FIG. 37 shows structure of still another power output apparatus asanother modification of the fifth embodiment;

FIG. 38 shows structure of another power output apparatus as a sixthembodiment of the present invention;

FIG. 39 is a nomogram showing the relationship between the revolvingspeed and the torque of the three different shafts linked with theplanetary gear in the power output apparatus of the sixth embodiment;

FIG. 40 is a nomogram showing the relationship between the revolvingspeed and the torque of the three different shafts linked with theplanetary gear in the power output apparatus of the sixth embodiment;

FIG. 41 shows structure of another power output apparatus as amodification of the sixth embodiment;

FIG. 42 shows structure of still another power output apparatus asanother modification of the sixth embodiment;

FIG. 43 shows an exemplified structure when the essential structure ofthe first through the third embodiments is applied to the vehicle with afour-wheel drive; and

FIG. 44 shows an exemplified structure when the essential structure ofthe fifth embodiment is applied to the vehicle with a four-wheel drive.

DETAILED DESCRIPTION OF THE INVENTION

Preferable embodiments of the present invention are described hereafter.FIG. 1 is a schematic view illustrating structure of a power outputapparatus 20 as a first embodiment according to the present invention;FIG. 2 is a cross sectional view illustrating detailed structures of aclutch motor 30 and an assist motor 40 included in the power outputapparatus 20 of FIG. 1; and FIG. 3 is a schematic view illustratinggeneral structure of a vehicle with the power output apparatus 20 ofFIG. 1 incorporated therein. The general structure of the vehicle isdescribed first for the convenience of description.

Referring to FIG. 3, the vehicle is provided with an engine 50 driven bygasoline as a power source. The air ingested from an air supply systemvia a throttle valve 66 is mixed with fuel, that is, gasoline in thisembodiment, injected from a fuel injection valve 51. The air/fuelmixture is supplied into a combustion chamber 52 to be explosivelyignited and burned. Linear motion of a piston 54 pressed down by theexplosion of the air/fuel mixture is converted to rotational motion of acrankshaft 56. The throttle valve 66 is driven to open and close by anactuator 68. An ignition plug 62 converts a high voltage applied from anigniter 58 via a distributor 60 to a spark, which explosively ignitesand combusts the air/fuel mixture.

Operation of the engine 50 is controlled by an electronic control unit(hereinafter referred to as EFIECU) 70. The EFIECU 70 receivesinformation from various sensors, which detect operating conditions ofthe engine 50. These sensors include a throttle position sensor 67 fordetecting a valve travel or position BP of the throttle valve 66, amanifold vacuum sensor 72 for measuring a load applied to the engine 50,a water temperature sensor 74 for measuring the temperature of coolingwater in the engine 50, and a speed sensor 76 and an angle sensor 78mounted on the distributor 60 for measuring the revolving speed (thenumber of revolutions per a predetermined time period) and therotational angle of the crankshaft 56. A starter switch 79 for detectinga starting condition ST of an ignition key (not shown) is also connectedto the EFIECU 70. Other sensors and switches connecting with the EFIECU70 are omitted from the illustration.

The crankshaft 56 of the engine 50 is linked with a drive shaft 22 via aclutch motor 30 and an assist motor 40 (described later in detail). Thedrive shaft 22 further connects with a differential gear 24, whicheventually transmits the torque output from the drive shaft 22 of thepower output apparatus 20 to left and right driving wheels 26 and 28.The clutch motor 30 and the assist motor 40 are driven and controlled bya controller 80. The controller 80 includes an internal control CPU andreceives inputs from a gearshift position sensor 84 attached to agearshift 82 and an accelerator position sensor 65 attached to anaccelerator pedal 64, as described later in detail. The controller 80sends and receives a variety of data and information to and from theEFIECU 70 through communication. Details of the control procedureincluding a communication protocol will be described later.

Referring to FIG. 1, the power output apparatus 20 essentially includesthe engine 50 for generating power, the clutch motor 30 with an outerrotor 32 and an inner rotor 34, the assist motor 40 with a rotor 42, andthe controller 80 for driving and controlling the clutch motor 30 andthe assist motor 40. The outer rotor 32 of the clutch motor 30 ismechanically connected to one end of the crankshaft 56 of the engine 50,whereas the inner rotor 34 thereof is mechanically linked with the rotor42 of the assist motor 40.

Structures of the clutch motor 30 and the assist motor 40 are describedbriefly. As shown in FIG. 1, the clutch motor 30 is constructed as asynchronous motor having permanent magnets 35 attached to an innersurface of the outer rotor 32 and three-phase coils 36 wound on slotsformed in the inner rotor 34. Power is supplied to the three-phase coils36 via a rotary transformer 38. Laminated sheets of non-directionalelectromagnetic steel are used to form teeth and slots for thethree-phase coils 36 in the inner rotor 34. A resolver 39 for measuringa rotational angle θe of the crankshaft 56 is attached to the crankshaft56. The resolver 39 may also serve as the angle sensor 78 mounted on thedistributor 60.

The assist motor 40 is also constructed as a synchronous motor havingthree-phase coils 44, which are wound on a stator 43 fixed to a casing45 to generate a revolving magnetic field. The stator 43 is also made oflaminated sheets of non-directional electromagnetic steel. A pluralityof permanent magnets 46 are attached to an outer surface of the rotor42. In the assist motor 40, interaction between a magnetic field formedby the permanent magnets 46 and a revolving magnetic field formed by thethree-phase coils 44 results in rotations of the rotor 42. The rotor 42is mechanically linked with the drive shaft 22 working as the torqueoutput shaft of the power output apparatus 20. A resolver 48 formeasuring a rotational angle θd of the drive shaft 22 is attached to thedrive shaft 22, which is further supported by a bearing 49 held in thecasing 45.

The inner rotor 34 of the clutch motor 30 is mechanically linked withthe rotor 42 of the assist motor 40 and further with the drive shaft 22.The rotation and axial torque of the crankshaft 56 of the engine 50 areaccordingly transmitted via the outer rotor 32 and the inner rotor 34 ofthe clutch motor 30 to the drive shaft 22 while the rotation and torqueof the assist motor 40 are added to or subtracted from the transmittedrotation and torque.

While the assist motor 40 is constructed as a conventional permanentmagnet-type three-phase synchronous motor, the clutch motor 30 includestwo rotating elements or rotors, that is, the outer rotor 32 with thepermanent magnets 35 mounted thereon and the inner rotor 34 with thethree-phase coils 36 attached thereto. The detailed structure of theclutch motor 30 is described according to the cross sectional view ofFIG. 2. The outer rotor 32 of the clutch motor 30 is attached to acircumferential end of a wheel 57 set around the crankshaft 56, by meansof a pressure pin 59a and a screw 59b. A central portion of the wheel 57is protruded to form a shaft-like element, to which the inner rotor 34is rotatably attached by means of bearings 37A and 37B. One end of thedrive shaft 22 is fixed to the inner rotor 34.

A plurality of permanent magnets 35, four in this embodiment, areattached to the inner surface of the outer rotor 32 as mentionedpreviously. The permanent magnets 35 are magnetized in the directiontowards the axial center of the clutch motor 30 and have magnetic polesof alternately inverted directions. The three-phase coils 36 of theinner rotor 34 facing to the permanent magnets 35 across a little gapare wound on a total of 24 slots (not shown) formed in the inner rotor34. Supply of electricity to the respective coils forms magnetic fluxesrunning through the teeth (not shown), which separate the slots from oneanother. Supply of a three-phase alternating current to the respectivecoils rotates this magnetic field. The three-phase coils 36 areconnected to receive electric power supplied from the rotary transformer38. The rotary transformer 38 includes primary windings 38A fixed to thecasing 45 and secondary windings 38B attached to the drive shaft 22coupled with the inner rotor 34. Electromagnetic induction enableselectric power to be transmitted from the primary windings 38A to thesecondary windings 38B or vice versa. The rotary transformer 38 haswindings for the three phases, that is, U, V, and W phases, to allow forthe transmission of three-phase electric currents.

Interaction between a magnetic field formed by one adjoining pair ofpermanent magnets 35 and a revolving magnetic field formed by thethree-phase coils 36 of the inner rotor 34 leads to a variety ofbehaviors of the outer rotor 32 and the inner rotor 34. The frequency ofthe three-phase alternating current supplied to the three-phase coils 36is generally equal to a difference between the revolving speed (thenumber of revolutions per second) of the outer rotor 32 directlyconnected to the crankshaft 56 and the revolving speed of the innerrotor 34. This results in a slip between the rotations of the outerrotor 32 and the inner rotor 34. Details of the control procedures ofthe clutch motor 30 and the assist motor 40 will be described later,based on the flowcharts.

As mentioned above, the clutch motor 30 and the assist motor 40 aredriven and controlled by the controller 80. Referring back to FIG. 1,the controller 80 includes a first driving circuit 91 for driving theclutch motor 30, a second driving circuit 92 for driving the assistmotor 40, a control CPU 90 for controlling both the first and the seconddriving circuits 91 and 92, and a battery 94 including a number ofsecondary cells. The control CPU 90 is a one-chip microprocessorincluding a RAM 90a used as a working memory, a ROM 90b in which variouscontrol programs are stored, an input/output port (not shown), and aserial communication port (not shown) through which data are sent to andreceived from the EFIECU 70. The control CPU 90 receives a variety ofdata via the input port. The input data include a rotational angle θe ofthe crankshaft 56 of the engine 50 measured with the resolver 39, arotational angle θd of the drive shaft 22 measured with the resolver 48,an accelerator pedal position AP (step-on amount of the acceleratorpedal 64) output from the accelerator position sensor 65, a gearshiftposition SP output from the gearshift position sensor 84, clutch motorcurrents Iuc and Ivc from two ammeters 95 and 96 disposed in the firstdriving circuit 91, assist motor currents Iua and Iva from two ammeters97 and 98 disposed in the second driving circuit 92, and a remainingcharge BRM of the battery 94 measured with a remaining charge meter 99.The remaining charge meter 99 may determine the remaining charge BRM ofthe battery 94 by any known method; for example, by measuring thespecific gravity of an electrolytic solution in the battery 94 or thewhole weight of the battery 94, by computing the currents and time ofcharge and discharge, or by causing an instantaneous short-circuitbetween terminals of the battery 94 and measuring an internal resistanceagainst the electric current.

The control CPU 90 outputs a first control signal SW1 for driving sixtransistors Tr1 through Tr6 working as switching elements of the firstdriving circuit 91 and a second control signal SW2 for driving sixtransistors Tr11 through Tr16 working as switching elements of thesecond driving circuit 92. The six transistors Tr1 through Tr6 in thefirst driving circuit 91 constitute a transistor inverter and arearranged in pairs to work as a source and a drain with respect to a pairof power lines L1 and L2. The three-phase coils (U,V,W) 36 of the clutchmotor 30 are connected via the rotary transformer 38 to the respectivecontacts of the paired transistors. The power lines L1 and L2 arerespectively connected to plus and minus terminals of the battery 94.The first control signal SW1 output from the control CPU 90 thussuccessively controls the power-on time of the paired transistors Tr1through Tr6. The electric current flowing through each coil 36 undergoesPWM (pulse width modulation) to give a quasi-sine wave, which enablesthe three-phase coils 36 to form a revolving magnetic field.

The six transistors Tr11 through Tr16 in the second driving circuit 92also constitute a transistor inverter and are arranged in the samemanner as the transistors Tr1 through Tr6 in the first driving circuit91. The three-phase coils (U,V,W) 44 of the assist motor 40 areconnected to the respective contacts of the paired transistors. Thesecond control signal SW2 output from the control CPU 90 thussuccessively controls the power-on time of the paired transistors Tr11through Tr16. The electric current flowing through each coil 44undergoes PWM to give a quasi-sine wave, which enables the three-phasecoils 44 to form a revolving magnetic field.

The power output apparatus 20 thus constructed works in accordance withthe operation principles discussed below, especially with the principleof torque conversion. By way of example, it is assumed that thecrankshaft 56 of the engine 50 driven by the EFIECU 70 rotates at arevolving speed (the number of revolutions per a predetermined timeperiod) Ne, which is equal to a predetermined value N1. In thedescription below, the revolving speed Ne of the crankshaft 56 is alsoreferred to as the revolving speed Ne of the engine 50. While thetransistors Tr1 through Tr6 in the first driving circuit 91 are in OFFposition, the controller 80 does not supply any electric current to thethree-phase coils 36 of the clutch motor 30 via the rotary transformer38. No supply of electric current causes the outer rotor 32 of theclutch motor 30 to be electromagnetically disconnected from the innerrotor 34. This results in racing the crankshaft 56 of the engine 50.Under the condition that all the transistors Tr1 through Tr6 are in OFFposition, there is no regeneration of energy from the three-phase coils36, and the engine 50 is kept at an idle.

As the control CPU 90 of the controller 80 outputs the first controlsignal SW1 to control on and of f the transistors Tr1 through Tr6 in thefirst driving circuit 91, a constant electric current flows through thethree-phase coils 36 of the clutch motor 30, based on the differencebetween the revolving speed Ne of the engine 50 and a revolving speed Ndof the drive shaft 22 (in other words, a difference Nc (=Ne-Nd) betweenthe revolving speed of the outer rotor 32 and that of the inner rotor 34in the clutch motor 30). A certain slip accordingly exists between theouter rotor 32 and the inner rotor 34 connected with each other in theclutch motor 30. At this moment, the inner rotor 34 rotates at therevolving speed Nd, which is lower than the revolving speed Ne of theengine 50. In this state, the clutch motor 30 functions as a generatorand carries out the regenerative operation to regenerate an electriccurrent via the first driving circuit 91. In order to allow the assistmotor 40 to consume energy identical with the electrical energyregenerated by the clutch motor 30, the control CPU 90 controls on andoff the transistors Tr11 through Tr16 in the second driving circuit 92.The on-off control of the transistors Tr11 through Tr16 enables anelectric current to flow through the three-phase coils 44 of the assistmotor 40, and the assist motor 40 consequently carries out the poweroperation to produce a torque.

Referring to FIG. 4, in the power output apparatus 20, when the engine50 is driven at a first driving point P1, where the engine speed Ne isequal to a predetermined revolving speed N1 and an engine torque Te isequal to a predetermined value T1, the clutch motor 30 carries out theregenerative operation to produce an energy defined by a first area G1.The energy of the first area G1 is supplied to the assist motor 40 as anenergy defined by a second area G2. The drive shaft 22 is accordinglydriven at a second driving point P2, where the drive shaft speed Nd isequal to a predetermined revolving speed N2 and a drive shaft torque Tdis equal to a predetermined value T2. The torque conversion is carriedout in the manner discussed above, and the energy corresponding to theslip in the clutch motor 30 or the revolving speed difference Nc(=Ne-Nd) is consequently given as a torque to the drive shaft 22.

In accordance with another example, it is assumed that the engine 50 isdriven at the second driving point P2, where the engine speed Ne isequal to the predetermined revolving speed N2 and the engine torque Teis equal to the predetermined value T2, while the revolving speed Nd ofthe drive shaft 22 is equal to the predetermined revolving speed N1,which is greater than the revolving speed N2. In this state, the innerrotor 34 of the clutch motor 30 rotates relative to the outer rotor 32in the direction of rotation of the drive shaft 22 at a revolving speeddefined by the absolute value of the revolving speed difference Nc(=Ne-Nd). The clutch motor 30 accordingly functions as a normal motorand consumes electric power to supply the energy of rotational motion tothe drive shaft 22. When the control CPU 90 of the controller 80controls the second driving circuit 92 to enable the assist motor 40 toregenerate electrical energy, a slip between the rotor 42 and the stator43 of the assist motor 40 makes the regenerative current flow throughthe three-phase coils 44. In order to allow the clutch motor 30 toconsume the energy regenerated by the assist motor 40, the control CPU90 controls both the first driving circuit 91 and the second drivingcircuit 92. This enables the clutch motor 30 to be driven without usingelectric power stored in the battery 94.

Referring back to FIG. 4, when the engine 50 is driven at the seconddriving point P2, where the revolving speed Ne=N2 and the torque Te=T2,the assist motor 40 regenerates an energy corresponding to the sum ofthe second area G2 and a third area G3. The energy of the areas G2 andG3 is supplied to the clutch motor 30 as an energy defined by the sum ofthe first area G1 and the third area G3. The drive shaft 22 isaccordingly driven at the first driving point P1, where the revolvingspeed Nd=N1 and the torque Td=T1.

Other than the torque conversion discussed above, the power outputapparatus 20 of the embodiment can charge the battery 94 with an excessof electrical energy or discharge the battery 94 to supplement theelectrical energy. This is implemented by controlling the mechanicalenergy output from the engine 50 (that is, the product of the torque Teand the revolving speed Ne), the electrical energy regenerated orconsumed by the clutch motor 30, and the electrical energy consumed orregenerated by the assist motor 40. The power (energy) output from theengine 50 can thus be transmitted to the drive shaft 22 at a higherefficiency.

The concrete procedure of torque conversion executed by the power outputapparatus 20 is described according to a torque control routine shown inthe flowchart of FIG. 5. The torque control routine is executedrepeatedly at predetermined time intervals after the driver has startedthe vehicle.

When the program enters the torque control routine, the control CPU 90of the controller 80 first receives data of revolving speed Nd of thedrive shaft 22 at step S100. The revolving speed Nd of the drive shaft22 can be computed from the rotational angle θd of the drive shaft 22read from the resolver 48. At subsequent step S101, the control CPU 90reads the accelerator pedal position AP detected by the acceleratorposition sensor 65. The driver steps on the accelerator pedal 64 whenfeeling insufficiency of output torque. The value of the acceleratorpedal position AP accordingly represents the desired output torque (thatis, desired torque of the drive shaft 22) which the driver requires. Theprogram then goes to step S102 at which the control CPU 90 computes atarget output torque Td* corresponding to the input accelerator pedalposition AP. The target output torque Td* implies a target torque to beoutput to the drive shaft 22 and is hereinafter referred to as the`output torque command value`. In this embodiment, output torque commandvalues Td* corresponding to the respective accelerator pedal positionsAP have been set in advance and stored in the ROM 90b. In response to aninput of the accelerator pedal position AP, the output torque commandvalue Td* corresponding to the input accelerator pedal position AP isextracted from the output torque command values Td* stored in the ROM90b.

At step S103, an amount of energy Pd (target energy) to be output to thedrive shaft 22 is calculated from the extracted output torque commandvalue Td* and the input revolving speed Nd of the drive shaft 22according to the equation of Pd=Td*×Nd. The program then proceeds tostep S104 at which the control CPU 90 sets a target engine torque Te*and a target engine speed Ne* of the engine 50 based on the outputenergy Pd thus obtained. The energy supplied from the engine 50 is equalto the product of the torque Te and the revolving speed Ne of the engine50, so that the relationship between the output energy Pd, the targetengine torque Te*, and the target engine speed Ne* can be defined asPd=Te*×Ne*. There are, however, numerous combinations of the targetengine torque Te* and the target engine speed Ne* of the engine 50satisfying the above relationship. In this embodiment, favorablecombinations of the target torque Te* and the target revolving speed Ne*of the engine 50 are experimentally or otherwise determined in advancefor the respective amounts of output energy Pd. In such favorablecombinations, the engine 50 is driven at highest possible efficiency andthe driving state of the engine 50 is smoothly varied with a variationin output energy Pd. The predetermined favorable combinations are storedin the form of a map in the ROM 90b. In practice, the target torque Te*and the target revolving speed Ne* of the engine 50 corresponding to theoutput energy Pd obtained at step S103 is read from the map at stepS104. The following gives a further description of the map.

FIG. 6 is a graph showing driving points of the engine 50 (defined bythe target engine torque Te* and the target engine speed Ne*) with theirefficiencies. The curve B in FIG. 6 represents a boundary of anengine-operable range, in which the engine 50 can be driven. In theengine-operable range, efficiency curvesr such as curves α1 through α6,can be drawn by successively joining the driving points having theidentical efficiency. In the engine-operable range, constant-outputenergy curves, such as curves C1--C1 through C3--C3, can also be drawnon each curve of constant-output energy, the energy output from theengine 50 and defined as the product of the torque Te and the revolvingspeed Ne is constant. The graph of FIG. 7 shows the efficiency of therespective driving points along the constant-output energy curves C1--C1through C3--C3 plotted against the revolving speed Ne of the engine 50.

Referring to FIG. 7, the efficiency with respect to the same outputenergy from the engine 50 is significantly varied by the driving pointof the engine 50. On the constant-output energy curve C1--C1, forexample, the efficiency of the engine 50 reaches its maximum when theengine 50 is driven at a driving point A1 (torque Te1 and revolvingspeed Ne1). Such a driving point attaining the highest possibleefficiency exists on each constant-output energy curve; a driving pointA2 for the constant-output energy curve C2--C2 and a driving point A3for the constant-output energy curve C3--C3. The curve A in FIG. 6 isobtained by joining such driving points attaining the highest possibleefficiency of the engine 50 for the respective amounts of output energyPd by a continuous curve. The map representing the relationship betweeneach driving point (torque Te and revolving speed Ne) on the curve A andthe output energy Pd is used at step S104 in the flowchart of FIG. 5 forsetting the target torque Te* and the target revolving speed Ne* of theengine 50.

The curve A should be continuous because of the following reason. Incase that discontinuous curves are used to set the driving point of theengine 50 against a variation in output energy Pd, the driving state ofthe engine 50 is abruptly varied with a variation in output energy Pdcrossing over the discontinuous driving points. The abrupt variation mayprevent the driving state from being smoothly shifted to a target leveland thereby cause knocking or another undesirable condition. Eachdriving point on the curve A may accordingly not correspond to thedriving point attaining the highest possible efficiency on the curve ofoutput energy Pd=constant.

After setting the target torque Te* and the target revolving speed Ne*of the engine 50, the program proceeds to steps S108, S110, and S111 tocontrol the clutch motor 30, the assist motor 40, and the engine 50based on the target engine torque Te* and the target engine speed Ne*,respectively. As a matter of convenience of illustration, the controloperations of the clutch motor 30, the assist motor 40, and the engine50 are shown as separate steps. In the actual procedure, however, thesecontrol operations are carried out simultaneously. By way of example,the control CPU 90 simultaneously controls the clutch motor 30 and theassist motor 40 by utilizing an interrupting process, while transmittingan instruction to the EFIECU 70 through communication in order to allowthe EFIECU 70 to control the engine 50 concurrently. The concreteprocedures of the control are described below.

FIG. 8 is a flowchart showing details of the control process of theclutch motor 30 executed at step S108 in the flowchart of FIG. 5. Whenthe program enters the clutch motor control routine, the control CPU 90of the controller 80 first reads the revolving speed Ne of the engine 50at step S112. The revolving speed Ne of the engine 50 may be calculatedfrom the rotational angle θe of the crankshaft 56 read from the resolver39 or directly measured with the speed sensor 76 mounted on thedistributor 60. In case that the speed sensor 76 is used, the controlCPu 90 receives data of revolving speed Ne from the EFIECU 70 connectingwith the speed sensor 76 through communication.

At subsequent step S113, a target clutch torque or torque command valueTc* of the clutch motor 30 is then calculated according to Equation (1)given below:

    Tc*=kc(Ne-Ne*)+Te*                                         (1)

wherein kc represents a coefficient of proportionality.

The torque command value Tc* of the clutch motor 30 is varied accordingto the deviation of the actual revolving speed Ne of the engine 50 fromthe target engine speed Ne*, in order to enable the engine 50 to bedriven stably at the driving point of the target engine torque Te* andthe target engine speed Ne*. Even when it is desirable to drive theengine 50 at the driving point of the target engine torque Te* and thetarget engine speed Ne*, since the torque Te of the engine 50corresponds to the reaction against the loading torque Tc of the clutchmotor 30, the function of the engine 50 alone does not allow the engine50 to be driven at the desired driving point. Compared with the clutchmotor 30 and the assist motor 40, the driving state of the engine 50 isfluctuated more significantly. Even when the actual torque Tc of theclutch motor 30 is set equal to the target engine torque Te* and thetorque Te of the engine 50 is thereby made identical with the targetengine torque Te*, the revolving speed Ne of the engine 50 may not becoincident with the target engine speed Ne*. The structure of theembodiment accordingly does not set the torque command value Tc* of theclutch motor 30 equal to the target engine torque Te* of the engine 50,but introduces a correction term based on the difference between theactual revolving speed Ne of the engine 50 and the target engine speedNe*.

The graph of FIG. 9 shows the relationship between the torque commandvalue Tc* of the clutch motor 30 and the target torque Te* and thetarget revolving speed Ne* of the engine 50. Referring to FIG. 9, whenthe revolving speed Ne of the engine 50 is greater than the targetengine speed Ne*, the torque command value Tc* is set equal to a valuegreater than the target engine torque Te*, in order to allow the clutchmotor 30 to reduce the revolving speed Ne of the engine 50. When therevolving speed Ne of the engine 50 is less than the target engine speedNe*, on the contrary, the torque command value Tc* is set equal to avalue smaller than the target engine torque Te*, in order to allow theclutch motor 30 to enhance the revolving speed Ne of the engine 50.

Referring back to the flowchart of FIG. 8, the control CPU 90 reads therotational angle θd of the drive shaft 22 from the resolver 48 at stepS114 and the rotational angle θe of the crankshaft 56 of the engine 50from the resolver 39 at step S115. The control CPU 90 then computes arelative angle θc of the drive shaft 22 to the crankshaft 56 by theequation of θc=θe-θd at step S116.

The program proceeds to step S118, at which the control CPU 90 reads theclutch motor currents Iuc and Ivc, which respectively flow through the Uphase and V phase of the three-phase coils 36 in the clutch motor 30 andare measured by the ammeters 95 and 96. Although the currents naturallyflow through all the three phases U, V, and W, measurement is requiredonly for the currents passing through the two phases since the sum ofthe currents is equal to zero. At subsequent step S120, the control CPU90 executes transformation of coordinates (three-phase to two-phasetransformation) using the values of currents flowing through the threephases obtained at step S118. The transformation of coordinates maps thevalues of currents flowing through the three phases to the values ofcurrents passing through d and q axes of the permanent magnet-typesynchronous motor and is executed according to Equation (2) given below:##EQU1##

The transformation of coordinates is carried out because the currentsflowing through the d and q axes are essential for the torque control inthe permanent magnet-type synchronous motor. Alternatively, the torquecontrol may be executed directly with the currents flowing through thethree phases. After the transformation to the currents of two axes, thecontrol CPU 90 computes deviations of currents Idc and Iqc actuallyflowing through the d and q axes from current command values Idc* andIqc* of the respective axes, which are calculated from the torquecommand value Tc* of the clutch motor 30, and subsequently determinesvoltage command values Vdc and Vqc with respect to the d and q axes atstep S122. In accordance with a concrete procedure, the control CPU 90executes arithmetic operations of Equations (3) and Equations (4) givenbelow:

    ΔIdc=Idc*-Idc

    ΔIqc=Iqc*-Iqc                                        (3)

    Vdc=Kp1·ΔIdc+ΣKi1·ΔIdc

    Vqc=Kp2·ΔIqc+ΣKi2·ΔIqc (4)

wherein Kp1, Kp2, Ki1, and Ki2 represent coefficients, which areadjusted to be suited to the characteristics of the motor applied. Eachvoltage command value Vdc (Vqc) includes a part in proportion to thedeviation ΔI from the current command value I* (the first term in theright side of Equation (4)) and a summation of historical data of thedeviations ΔI for `i` times (the second term in the right side). Thecontrol CPU 90 then re-transforms the coordinates of the voltage commandvalues thus obtained (two-phase to three-phase transformation) at stepS124. This corresponds to an inverse of the transformation executed atstep S120. The inverse transformation determines voltages Vuc, Vvc, andVwc actually applied to the three-phase coils 36 as expressed byEquations (5) given below: ##EQU2##

The actual voltage control is accomplished by on-off operation of thetransistors Tr1 through Tr6 in the first driving circuit 91. At stepS126, the on- and off-time of the transistors Tr1 through Tr6 in thefirst driving circuit 91 is PWM (pulse width modulation) controlled inorder to attain the voltage command values Vuc, Vvc, and Vwc determinedby Equations (5) above.

The torque command value Tc* is positive when a positive torque isapplied to the drive shaft 22 in the direction of rotation of thecrankshaft 56. By way of example, it is assumed that a positive value isset to the torque command value Tc*. When the revolving speed Ne of theengine 50 is greater than the revolving speed Nd of the drive shaft 22on this assumption, that is, when the revolving speed difference Nc(=Ne-Nd) is positive, the clutch motor 30 is controlled to carry out theregenerative operation and produce a regenerative current according tothe revolving speed difference Nc. When the revolving speed Ne of theengine 50 is lower than the revolving speed Nd of the drive shaft 22,that is, when the revolving speed difference Nc (=Ne-Nd) is negative, onthe contrary, the clutch motor 30 is controlled to carry out the poweroperation and rotate relative to the crankshaft 56 in the direction ofrotation of the drive shaft 22 at a revolving speed defined by theabsolute value of the revolving speed difference Nc. For the positivetorque command value Tc*, both the regenerative operation and the poweroperation of the clutch motor 30 implement the identical switchingcontrol. In accordance with a concrete procedure, the transistors Tr1through Tr6 of the first driving circuit 91 are controlled to enable apositive torque to be applied to the drive shaft 22 by the combinationof the magnetic field generated by the permanent magnets 35 set on theouter rotor 32 with the revolving magnetic field generated by thecurrents flowing through the three-phase coils 36 mounted on the innerrotor 34 of the clutch motor 30. The identical switching control isexecuted for both the regenerative operation and the power operation ofthe clutch motor 30 as long as the sign of the torque command value Tc*is not changed. The clutch motor control routine of FIG. 8 is thusapplicable to both the regenerative operation and the power operation.Under the condition of braking the drive shaft 22 or moving the vehiclein reverse, the torque command value Tc* has the negative sign. Theclutch motor control routine of FIG. 8 is also applicable to the controlprocedure under such conditions. when the relative angle θc obtained atstep S116 is varied in the reverse direction.

FIGS. 10 and 11 are flowcharts showing details of the torque controlprocess of the assist motor 40 executed at step S110 in the flowchart ofFIG. 5. When the program enters the assist motor control routine, thecontrol CPU 90 first reads the revolving speed Nd of the drive shaft 22at step S131 and the revolving speed Ne of the engine 50 at step S132.The control CPU 90 then calculates a revolving speed difference Ncbetween the input data of revolving speed Nd of the drive shaft 22 andrevolving speed Ne of the engine 50 (Nc=Ne-Nd) at step S133, and checksthe sign of the revolving speed difference Nc thus obtained at stepS134.

When the revolving speed difference Nc has the positive sign, the clutchmotor 30 is under regenerative control and the program proceeds to stepS135, at which a power Pc regenerated by the clutch motor 30 iscalculated according to Equation (6) given below. At subsequent stepS136, the control CPU 90 calculates a torque command value Ta* of theassist motor 40 that consumes the regenerative power Pc, according toEquation (7) given below:

    Pc=Ksc×Nc×Tc*                                  (6)

    Ta*=Ksa×Pc/Nd                                        (7)

wherein Ksc in Equation (6) represents the efficiency of the clutchmotor 30 and Ksa in Equation (7) the efficiency of the assist motor 40.

When the revolving speed difference Nc has the negative sign, on theother hand, the clutch motor 30 is under power control and the programproceeds to step S137, at which a power Pc consumed by the clutch motor30 is calculated according to Equation (8) given below. At subsequentstep S138, the control CPU 90 calculates a torque command value Ta* ofthe assist motor 40 that regenerates the consumed power Pc, according toEquation (9) given below. When the revolving speed difference Nc isnegative, the power Pc and the torque command value Ta* are alsonegative and the assist motor 40 applies the torque in reverse of therotation to the drive shaft 22. The assist motor 40 is accordingly underregenerative control. Although the efficiency Ksc of the clutch motor 30and the efficiency Ksa of the assist motor 40 in Equations (6) and (7)are also included in Equations (8) and (9), different efficiencies maybe applied to the regenerative operation and the power operation inmotors having different efficiencies of regenerative operation and poweroperation.

    Pc=(1/Ksc)×Nc×Tc*                              (8)

    Ta*=(1/Ksa)×Pc/Nd                                    (9)

After the processing of step S136 or S138, the program proceeds to stepS139, at which the torque command value Ta* thus calculated is comparedwith a maximum torque Tamax which the assist motor 40 can apply. Whenthe torque command value Ta* exceeds the maximum torque Tamax, thetorque command value Ta* is restricted to and set equal to the maximumtorque Tamax at step S140.

The control CPU 90 then reads the rotational angle θd of the drive shaft22 from the resolver 48 at step S141, and receives data of assist motorcurrents Iua and Iva at step S142, which respectively flow through the Uphase and V phase of the three-phase coils 44 in the assist motor 40 andare measured with the ammeters 97 and 98. The control CPU 90 thenexecutes transformation of coordinates for the currents of the threephases at step S144, computes voltage command values Vda and Vqa at stepS146, and executes inverse transformation of coordinates for the voltagecommand values at step S148. At subsequent step S150, the control CPU 90determines the on- and off-time of the transistors Tr11 through Tr16 inthe second driving circuit 92 for PWM (pulse width modulation) control.The processing executed at steps S144 through S150 is similar to thatexecuted at steps S120 through S126 of the clutch motor control routineshown in the flowchart of FIG. 8.

The control of the engine 50 (step S111 in the flowchart of FIG. 5) isexecuted in the following manner. In order to attain stationary drivingat the driving point defined by the target engine torque Te* and thetarget engine speed Ne* set at step S104 in FIG. 5, the control CPU 90regulates the torque Te and the revolving speed Ne of the engine 50. Inaccordance with a concrete procedure, the control CPU 90 transmits thetarget torque Te* and the target revolving speed Ne* of the engine 50 tothe EFIECU 70 through communication, and the EFIECU 70 controls theposition of the throttle valve 66 and fuel injection from the fuelinjection valve 51 based on the target engine torque Te* and the targetengine speed Ne*. The position of the throttle valve 66 is controlled,for example, according to a throttle valve position control routineshown in FIG. 12, whereas the fuel injection control is carried out, forexample, according to a fuel injection control routine shown in FIG. 13.These routines are repeatedly executed at predetermined time intervals.The following describes these routines in brief.

When the program enters the throttle valve position control routineshown in the flowchart of FIG. 12, the EFIECU 70 first reads theposition BP of the throttle valve 66 measured with the throttle valveposition sensor 67 at step S152 and the revolving speed Ne of the engine50 at step S154. The revolving speed Ne of the engine 50 supplied to theEFIECU 70 is typically measured with the speed sensor 76 mounted on thedistributor 60. In case that the revolving speed Ne of the engine 50 iscalculated from the rotational angle θe of the crankshaft 56 read fromthe resolver 39, the EFIECU 70 receives the data of rotational angle θefrom the controller 80 through communication.

At subsequent step S156, the EFIECU 70 sets a standard position BPF ofthe throttle valve 66 based on the output energy Pd obtained at stepS103 in the flowchart of FIG. 5. In this embodiment, the positions BP ofthe throttle valve 66 to attain stationary driving of the engine 50 atthe driving point of the target engine torque Te* and the target enginespeed Ne* are experimentally or otherwise determines for the respectiveamounts of output energy Pd. The relationship thus obtained ispreviously stored as a map in a ROM (not shown) included in the EFIECU70. The position BP corresponding to the given output energy Pd is readfrom the map as the standard position BPF.

At step S158, the EFIECU 70 then calculates a position command value BP*from the standard position BPF, the revolving speed Ne, and the targetengine speed Ne* according to Equation (10) given below:

    BP*=ke(Ne*-Ne)+BPF                                         (10)

wherein ke represents a constant of proportionality. The positioncontrol value BP* is set in this manner, so that the engine 50 is stablydriven at the target engine speed Ne*.

After setting the position command value BP*, the EFIECU 70 subtractsthe position BP from the position command value BP* to yield adifference ΔBP at step S160. The actuator 68 then works to drive thethrottle valve 66 by the difference ΔBP at step S162, and the programexits from the routine.

The following describes the fuel injection control executed according tothe fuel injection control routine shown in the flowchart of FIG. 13.When the program enters the routine, the EFIECU 70 first receives dataof revolving speed Ne of the engine 50 at step S164 and an amount ofintake air Q at step S166. The amount of intake air Q can be calculatedfrom the negative pressure in an intake manifold measured by themanifold vacuum sensor 72 and the revolving speed Ne of the engine 50.

At step S168, the EFIECU 70 then calculates a standard amount of fuelinjection TP from the resolving speed Ne and the amount intake air Qinput at steps S164 and S166 according to Equation (11) given below:

    TP=kt·Q/Ne                                        (11)

An actual amount of fuel injection TAU is then calculated at step S170by multiplying the standard amount of fuel injection TP by requiredcorrection coefficients according to Equation (12) given below:

    TAU=TP·FAF·FWL·α·β(12)

FAF, which represents an air/fuel ratio correction coefficient based ona lean-rich state of an air/fuel mixture detected by an air/fuel ratiosensor (not shown), gradually increases by integration until the outputof the air/fuel ratio sensor reaches a value corresponding to the richstate of the air/fuel mixture, and then gradually decreases byintegration until the output reaches a value corresponding to the leanstate. FWL represents a warm-up increase correction coefficient andtakes a value equal to or greater than 1.0 when the temperature ofcooling water is not higher than 60° C. α and β represent othercorrection coefficients relating to, for example, intake temperaturecorrection, transient correction, and power voltage correction.

After calculating the actual amount of fuel injection TAU at step S170,the program proceeds to step S172 to set a fuel injection timecorresponding to the actual amount of fuel injection TAU on a counter(not shown) that determines an opening time period, for which the fuelinjection valve 51 is open. The program then enters a fuel injectionvalve driving routine (not shown) to drive and open the fuel injectionvalve 51 for the opening time period preset on the counter and to enablea required amount of fuel to be injected into an intake port of theengine 50.

As discussed above, the power output apparatus 20 of the embodimentselects a driving point attaining the highest possible efficiency amongthe respective driving points on each curve of constant energy outputfrom the engine 50, and sets the torque Te and the revolving speed Ne ateach selected driving point as the target engine torque Te* and thetarget engine speed Ne*. This enhances the efficiency of the engine 50and thereby the efficiency of the whole power output apparatus 20. Theselected driving points regarding the respective amounts of outputenergy can be joined with one another to form a continuous curve. Thedriving point of the engine 50 can thus be varied smoothly with a smallamount of variation in output energy Pd. This structure effectivelyprevents the engine 50 from undesirably stalling or stopping.

The power output apparatus 20 of the embodiment sets the torque commandvalue Tc* of the clutch motor 30 to lessen the difference between theactual revolving speed Ne of the engine 50 and the target engine speedNe*. This structure enables the engine 50 to be stably driven at thetarget engine speed Ne*. Adjustment of the position BP of the throttlevalve 66 is also carried out to reduce the difference between the actualrevolving speed Ne of the engine 50 and the target engine speed Ne*.Such adjustment further facilitates the stable operation of the engine50 at the target engine speed Ne*.

Although the driving points set as the target engine torque Te* and thetarget engine speed Ne* are continuous with respect to the amount ofoutput energy in the power output apparatus 20 of the embodiment, theymay be discontinuous as long as an abrupt change of the driving point ofthe engine 50 can be effectively avoided.

As mentioned above, the power output apparatus 20 of the embodiment setsthe torque command value Tc* of the clutch motor 30 to lessen thedifference between the actual revolving speed Ne of the engine 50 andthe target engine speed Ne*. The target torque Te* of the engine 50 may,however, be directly set as the torque command value Tc*. The positioncommand value BP* of the throttle valve 66 is also set to decrease thedifference between the actual revolving speed Ne of the engine 50 andthe target engine speed Ne*. The standard position BPF may, however, bedirectly set as the position command value BP*.

The power output apparatus 20 of the embodiment selects a driving pointattaining the highest possible efficiency among the respective drivingpoints on each curve of constant energy output from the engine 50, andsets the torque Te and the revolving speed Ne at each selected drivingpoint as the target engine torque Te* and the target engine speed Ne*.Another possible structure sets the torque Te and the revolving speed Neof a selected driving point, which attains the best possible emissionamong the respective driving points on each constant-output energycurve, as the target engine torque Te* and the target engine speed Ne*.This structure further improves the emission of the engine 50. Stillanother possible structure sets the torque Te and the revolving speed Neof a selected driving point, which has the smallest possible drivingnoise among the respective driving points on each constant-output energycurve, as the target engine torque Te* and the target engine speed Ne*.This structure further lessens the driving noise of the engine 50.

In the power output apparatus 20 of the embodiment, a map of theselected driving point, which attains the highest possible efficiencyamong the respective driving points on each constant-output energycurve, is used to set the target engine torque Te* and the target enginespeed Ne*. An alternative structure provides a plurality of maps, suchas a map of a driving point with the highest efficiency, that of adriving point with the best emission, and that of a driving point withthe smallest driving noise, and selects an appropriate map according tothe environment in which the vehicle runs. By way of example, a map ofthe driving point with the highest efficiency is selected while thevehicle runs in the suburbs; and a map of the driving point with thebest emission is selected while the vehicle runs in the town. Thisstructure realizes the appropriate operation of the engine 50 based onthe environment in which the vehicle runs. The user may select anappropriate map, for example, with a press of a selection button.

The power output apparatus 20 of the embodiment joins the selecteddriving points, which attain the highest possible efficiency among therespective driving points on the curves of constant energy output fromthe engine 50, with one another to yield a continuous curve, so as toprovide a map for setting the target torque Te* and the target revolvingspeed Ne* of the engine 50. In accordance with another possiblestructure, however, the target engine torque Te* and the target enginespeed Ne* may be set out of a predetermined range of driving points ofthe engine 50. In case that the vehicle or another equipment mounted onthe vehicle resonates in a specific range of revolving speed of theengine 50, for example, it may be desirable to avoid driving points inthis specific range of revolving speed (that is, resonant revolvingspeed range NF) when setting the target engine torque Te* and the targetengine speed Ne*. The driving points of the engine 50 for setting thetarget torque Te* and the target revolving speed Ne* in the resonantrevolving speed range NF are given as a curve D in FIG. 14. The curve Dis identical with the curve A in the graph of FIG. 6, except an area inthe vicinity of the resonant revolving speed range NF, that is a rangein which the revolving speed Ne of the engine 50 is varied from Nef1 toNef2. FIG. 15 is an enlarged view showing the area in the vicinity ofthe resonant revolving speed range NF.

Referring to FIG. 15, the curve D goes as points D1, D2, D3, and D4 inthe resonant revolving speed range NF and in its vicinity. A curve E--Eincluding the points D2 and D3 is a constant-output energy curve passingthrough a driving point Pef, which is on the curve A in the graph ofFIG. 6 at a median of the resonant revolving speed range NF. Variationin target engine torque Te* and target engine speed Ne* on the curve Dshifts the driving point of the engine 50 from the point D2 to the pointD3 or vice versa when the output energy Pd is varied across the curveE--E. This causes an abrupt change of the driving point of the engine50. Unless the resonant revolving speed range NF is significantly wide,the condition of the engine 50 can smoothly shift to the new drivingpoint without stalling or stopping the engine 50.

Setting the target torque Te* and the target revolving speed Ne* of theengine 50 out of the resonant revolving speed range NF can effectivelyprevents the vehicle or another equipment mounted on the vehicle fromresonating.

In the embodiment discussed above, the target torque Te* and the targetrevolving speed Ne* of the engine 50 are set out of the resonantrevolving speed range NF in which the vehicle or another equipmentmounted on the vehicle resonates. Other possible structures may,however, set the target torque Te* and the target revolving speed Ne* ofthe engine 50 out of a predetermined torque range, out of apredetermined revolving speed range and predetermined torque range (thatis, a predetermined range of driving points), or out of a range ofdriving points in which the vehicle or another equipment mounted on thevehicle resonates with the driving noise of the engine 50.

The following describes another power output apparatus 20A as a secondembodiment according to the present invention. The structure of thepower output apparatus 20A of the second embodiment is identical withthat of the power output apparatus 20 of the first embodiment, and isthus not described specifically. The numerals and symbols used in thedescription of the first embodiment have the same meanings in the secondembodiment, unless otherwise specified.

The torque control in the power output apparatus 20A of the secondembodiment is carried out by executing a torque control routine shown inthe flowchart of FIG. 16, instead of the torque control routine in theflowchart of FIG. 5 executed by the power output apparatus 20 of thefirst embodiment.

When the program enters the torque control routine of FIG. 16, thecontrol CPU 90 of the controller 80 first reads the revolving speed Neof the engine 50 at step S180 and the revolving speed Nd of the driveshaft 22 at step S182. The control CPU 90 then reads the acceleratorpedal position AP measured by the accelerator position sensor 65 at stepS184, and determines the output torque command value Td* based on theinput accelerator pedal position AP at step S186.

The control CPU 90 calculates a desired output energy Pd by multiplyingthe output torque command value Td* by the revolving speed Nd of thedrive shaft 22 at step S188, and subsequently calculates an actualoutput energy Pe of the engine 50 by multiplying the torque commandvalue Tc* of the clutch motor 30 by the revolving speed Ne of the engine50 at step S190. The program then proceeds to step S192 to calculate adifference ΔPd between the desired output energy Pd and the actualoutput energy Pe. The torque command value Tc* of the clutch motor 30 isused for the calculation of the energy Pe actually output from theengine 550, because the torque Te of the engine 50 is not easilymeasured while it can be assumed that the torque Te of the engine 50 isequivalent to the torque Tc of the clutch motor 30, that is, the torquecommand value Tc*. The power output apparatus 20A of the secondembodiment also carries out the clutch motor control routine of thefirst embodiment shown in the flowchart of FIG. 8 as described later, sothat the torque command value Tc* of the clutch motor 30 is set at stepS113 in the flowchart of FIG. 8.

The difference ΔPd is then compared with a predetermined threshold valuePref at step S194. The threshold value Pref is set as an energydifference between driving points, which can smoothly increase theenergy Pe output from the engine 50 without stalling or stopping theengine 50. The threshold value Pref depends upon the characteristics ofthe engine and the map of the driving point. When the difference ΔPd isgreater than the threshold value Pref at step S194, the programdetermines that the shift from the current driving point of the engine50 to another driving point corresponding to the output energy Pd cannot be implemented smoothly. The program accordingly proceeds to stepS196 to add the threshold value Pref to the energy Pe actually outputfrom the engine 50 and set a new output energy Pd, prior to theprocessing of step S200. When the difference ΔPd is equal to or lessthan the threshold value Pref, on the contrary, the program determinesthat the shift from the current driving point of the engine 50 toanother driving point corresponding to the output energy Pd can beimplemented smoothly, and directly goes to step S200.

At step S200, the target torque Te* and the target revolving speed Ne*of the engine 50 are set using the preset output energy Pd and a mapcorresponding to that of the first embodiment shown in FIG. 6. Based onthe target engine torque Te* and the target engine speed Ne* thusobtained, the clutch motor 30, the assist motor 40, and the engine 50are controlled respectively at steps S202, S204, and S206. The concreteprocedures of steps S202 through S206 are identical with those of stepsS108 through S111 of the first embodiment shown in the flowchart of FIG.5. Like the first embodiment, although the control operations of theclutch motor 30, the assist motor 40, and the engine 50 are shown asseparate steps for the matter of convenience, these controls are carriedout simultaneously in the actual procedure.

This torque control enables the engine 50 to smoothly increase itsoutput energy Pe, even when the driver steps on the accelerator pedal 64to a relatively large depth. FIG. 17 shows the variations against timeunder such conditions. Referring to FIG. 17, by way of example, thedriver steps on the accelerator pedal 64 to a relatively large depth ata time point t1 to change the accelerator pedal position AP from a valueAP1 to another value AP2. The energy Pe actually output from the engine50 has values Pe1 and Pe2 respectively corresponding to the values AP1and AP2 of the accelerator pedal position AP. It is assumed here thatthe difference between the values Pe1 and Pe2 is remarkably larger thanthe threshold value Pref. The output energy Pd is then set at step S196in the flowchart of FIG. 16 by adding the threshold value Pref to theenergy Pe actually output from the engine 50, and is used for thecontrol procedures of the engine 50, the clutch motor 30, and the assistmotor 40. The energy Pe actually output from the engine 50 and thetorque Tc of the clutch motor 30 thus increase little by little. Therepetition of this processing enables the actual output energy Pe of theengine 50 to approach the value Pe2 and makes the difference between theactual output energy Pe and the value Pe2 equal to or less than thethreshold value Pref. Under such conditions, the output energy Pdcorresponding to the step-on amount of the accelerator pedal 64 isdirectly used for the control operations of the engine 50, the clutchmotor 30, and the assist motor 40. The actual output energy Pe of theengine 50 eventually becomes coincident with the value Pe2 at a timepoint t2.

When the driver steps on the accelerator pedal 64 by a relatively largeamount, the power output apparatus 20A of the second embodiment controlsthe engine 50, the clutch motor 30, and the assist motor 40, based onthe output energy at a driving point to which the engine 50 can smoothlyshift from the current driving point, instead of the output energy Pdcorresponding to the step-on amount of the accelerator pedal 64. Thisstructure enables the driving point of the engine 50 to be smoothlyshifted to the driving point giving the output energy Pd correspondingto the step-on amount of the accelerator pedal 64, thereby effectivelypreventing the engine 50 from stalling or stopping due to an abruptchange of the driving point of the engine 50.

Like the first embodiment, the power output apparatus 20A of the secondembodiment sets the torque Te and the revolving speed Ne at a specificdriving point, which attains the highest possible efficiency among therespective driving points on each constant-output energy curve of theengine 50, as the target engine torque Te* and the target engine speedNe*. This further enhances the operation efficiency of the engine 50 andthereby improves the efficiency of the whole power output apparatus 20A.

Although the power output apparatus 20A of the second embodiment usesthe predetermined threshold value Pref, the threshold value Pref may beset according to the energy currently output from the engine 50. Thisalternative structure enables the threshold value Pref to be set moresuitably for each driving point of the engine 50.

In the power output apparatus 20A of the second embodiment, when theoutput energy Pd is set by adding the threshold value Pref to the energyPe actually output from the engine 50, the control procedure is carriedout to enable the newly set output energy Pd to be applied to the driveshaft 22. In accordance with another possible structure, an insufficientamount of energy may be supplemented by the power stored in the battery94. In this case, the assist motor 40 is controlled according to anassist motor control routine shown in the flowchart of FIG. 18, insteadof the control routine of FIGS. 10 and 11. In the assist motor controlroutine of FIG. 18, the torque command value Ta* of the assist motor 40is set at step S210 by subtracting the torque command value Tc* of theclutch motor 30 set at step S113 in the clutch motor control routine ofFIG. 8 from the output torque command value Td* determined at step S186in the torque control routine of FIG. 16. The concrete procedures ofsteps S211 through S220 are identical with those of steps S141 throughS150 in the assist motor control routine of FIGS. 10 and 11. In casethat the step-on amount of the accelerator pedal 64 is remarkably variedand the engine 50 can not output the power corresponding to the step-onamount of the accelerator pedal 64, that is, even in the transientperiod while the driving point of the engine 50 is being shifted to anew target driving point for outputting the power corresponding to thestep-on amount of the accelerator pedal 64, this control procedure ofthe assist motor 40 enables the torque set as the output torque commandvalue Td* corresponding to the step-on amount of the accelerator pedal64 to be output to the drive shaft 22.

The following describes still another power output apparatus 20B as athird embodiment according to the present invention. The structure ofthe power output apparatus 20B of the third embodiment is identical withthat of the power output apparatus 20 of the first embodiment, and isthus not described specifically. The numerals and symbols used in thedescription of the first embodiment have the same meanings in the thirdembodiment, unless otherwise specified.

The power output apparatus 20B of the third embodiment executes thetorque control routine of FIG. 5 carried out by the power outputapparatus 20 of the first embodiment. The control procedure of theclutch motor 30 executed at step S108, however, follows a clutch motorcontrol routine shown in the flowcharts of FIGS. 19 and 20, in place ofthe clutch motor control routine of FIG. 8. Like the power outputapparatus 20 of the first embodiment, the control procedures of theassist motor 40 at step S110 and of the engine 50 at step S111 in thetorque control routine of FIG. 5 respectively follow the assist motorcontrol routine of FIGS. 10 and 11 and the throttle valve positioncontrol routine of FIG. 12 and the fuel injection control routine ofFIG. 13. The following mainly describes the difference between theclutch motor control routine of FIG. 8 executed by the power outputapparatus 20 of the first embodiment and that of FIGS. 19 and 20executed by the power output apparatus 20B of the third embodiment.

When the program enters the routine, the control CPU 90 of thecontroller 80 reads the torque Tc which the clutch motor 30 applies tothe drive shaft 22, that is, the torque command value Tc* currently setin the clutch motor 30, from the RAM 90a at step S230. Thecontrol CPU 90then receives data of rotational speed ω of the crankshaft 56 of theengine 50 (hereinafter referred to as the rotational speed of the engine50) at step S232. The rotational speed ω of the engine 50 may becalculated from the rotational angle θe of the crankshaft 56 which hasbeen read from the resolver 39, or alternatively calculated from therevolving speed Ne of the engine 50 (ω=2π×Ne). The program then proceedsto step S234, at which the control CPU 90 subtracts previous data ofrotational speed ω (previous ω) input in a previous cycle of thisroutine from the current data of rotational speed ω of the engine 50,and divides the difference by an interval Δt of activating this routine,so as to determine a change rate ω' of rotational speed of the engine50. This routine can be normally executed even immediately after a startof the vehicle, since the previous ω is initialized to zero in aninitialization routine (not shown) executed prior to this routine.

After calculating the change rate ω' of rotational speed of the engine50, the program proceeds to step S236 to calculate an estimated torqueTef, which the engine 50 is assumed to currently output, according toEquation (13) given below:

    Tef=Tc+1×ω'                                    (13)

The value `1` in the right side of Equation (13) represents the momentof inertia around the crankshaft 56, the outer rotor 32 linked with thecrankshaft 56, or the like. Equation (13) is led as an equation ofmotion, based on the equilibrium of forces acting on the crankshaft 56.Namely the torque Te of the engine 50 acting on the crankshaft 56 isequal to the sum of the torque Tc of the clutch motor 30 and the force(1×ω') expressed as the motion of acceleration in the system.

At subsequent step S238, the control CPU 90 reads a revolving speed(estimated target revolving speed) Nef* corresponding to the estimatedtorque Tef of the engine 50 from the map of FIG. 6 for determining thedriving point of the engine 50. For example, as shown in FIG. 21, theestimated target revolving speed Nef* is determined as a valuecorresponding to the estimated torque Tef on a curve A of driving pointsattaining the highest possible efficiency of the engine 50.

The torque command value Tc* of the clutch motor 30 is then calculatedat step S240 from the estimated torque Tef and the estimated targetrevolving speed Nef* according to Equation (14) given below:

    Tc*=Tef+kc(Ne-Nef*)+∫ki(Ne-Nef*)dt                    (14)

The second term in the right side of Equation (14) represents acorrection term based on the difference between the actual revolvingspeed Ne of the engine 50 and the estimated target revolving speed Nef*,wherein kc denotes a constant. The third term in the right side ofEquation (14) represents an integral term to cancel the stationarydeviation of the revolving speed Ne of the engine 50 from the estimatedtarget revolving speed Nef*, wherein ki denotes a constant. The clutchmotor 30 is controlled with the torque command value Tc* of the clutchmotor 30 thus obtained, so that the engine 50 is controlled to be drivenat a specific driving point where the torque Te is equal to theestimated torque Tef and the revolving speed Ne is equal to theestimated target revolving speed Nef*.

After setting the torque command value Tc* of the clutch motor 30, thecontrol CPU 90 of the controller 80 executes the processing of stepsS244 through S256 in the flowchart of FIG. 20. The concrete proceduresare identical with those of steps S114 through S126 in the clutch motorcontrol routine of FIG. 8 carried out by the power output apparatus 20of the first embodiment, and are thus not specifically described here.

FIG. 22 shows the operations in the power output apparatus 20B of thethird embodiment when the driver steps on the accelerator pedal 64 to arelatively large depth. By way of example, it is assumed that the driversteps on the accelerator pedal 64 by a relatively large amount at a timepoint t1 to change the accelerator pedal position AP from a value AP1 toanother value AP2. The change of the accelerator pedal position APcauses the target torque Te* and the target revolving speed Ne* of theengine 50 to be newly set based on the new accelerator pedal position APby the processing of steps S100 through S104 in the torque controlroutine of FIG. 5. The engine 50 is subsequently controlled at step S111in the same routine, based on the target engine torque Te* and thetarget engine speed Ne*. In order to drive the engine 50 at the drivingpoint defined by the target engine torque Te* and the target enginespeed Ne*, the throttle valve position control routine of FIG. 12 iscarried out to change the position BP of the throttle valve 66, whereasthe fuel injection control routine of FIG. 13 is carried out to vary theamount of fuel injection from the fuel injection valve 51.

The standard position BPF of the throttle valve 66 based on theaccelerator pedal position AP is set equal to a value BP2. Immediatelyafter a change of the accelerator pedal position AP, there is adifference between the actual revolving speed Ne of the engine 50 andthe target engine speed Ne*. The position BP of the throttle valve 66 iscorrected according to the difference and temporarily made greater thanthe value BP2. The position BP of the throttle valve 66 then graduallydecreases to the value BP2 as the revolving speed Ne of the engine 50approaches the target engine speed Ne*.

As discussed previously, the engine 50 has a poorer response than motorsand can thus not be driven at a target driving point immediately after achange of the position BP of the throttle valve 66. When the torque Tcof the clutch motor 30 acting as a loading torque of the engine 50 isset equal to the target engine torque Te* immediately after a change inaccelerator pedal position AP, the engine 50 may stall or even stop insome cases. The power output apparatus 20B of the third embodimentcarries out the clutch motor control routine of FIGS. 19 and 20 tocalculate the estimated torque Tef, which the engine 50 is assumed tocurrently output, from the revolving speed Ne of the engine 50 and setthe torque command value Tc* of the clutch motor 30 based on theestimated torque Tef and the estimated target revolving speed Nef* ledfrom the estimated torque Tef. The engine 50 accordingly shifts itsdriving point to a target driving point (point P*) along the curve Ashown in FIG. 21. Referring to FIG. 22, for example, at an arbitrarytime point t2 between the time point t1 when the accelerator pedalposition AP is varied and a time point t3 when the engine 50 is drivenat the driving point of the target engine torque Te* and the targetengine speed Ne*, the engine 50 is driven at a driving point defined bythe estimated torque Tef, which the engine 50 is assumed to currentlyoutput, and by the estimated target revolving speed Nef* correspondingto the estimated torque Tef and read from the map of FIG. 6.

As discussed above, the power output apparatus 20B of the thirdembodiment estimates the torque currently output from the engine 50, andcontrols the torque Tc of the clutch motor 30 in order to enable theengine 50 to be driven at the driving point attaining the highestpossible efficiency with respect to the estimated torque. The engine 50can thus be driven at driving points of the highest possible efficiency.In case that the target driving point of the engine 50 is a fixedstationary state, the engine 50 is stably driven at the target drivingpoint. When the target driving point is changed, the engine 50 issmoothly shifted to the new target driving point along the path ofhigh-efficiency driving points. With a change of the target drivingpoint, the position BP of the throttle valve 66 is immediately varied toa value corresponding to the new target driving point, so that theengine 50 can be quickly shifted to the new target driving point.

Like the first embodiment, the power output apparatus 20B of the thirdembodiment sets the torque Te and the revolving speed Ne at a specificdriving point, which attains the highest possible efficiency among therespective driving points on each constant-output energy curve of theengine 50, as the target engine torque Te* and the target engine speedNe*. This further enhances the operation efficiency of the engine 50 andthereby improves the efficiency of the whole power output apparatus 20B.

In the power output apparatus 20B of the third embodiment, the controlprocedure of the assist motor 40 executed at step S110 in the torquecontrol routine of FIG. 5 follows the assist motor control routine shownin FIGS. 10 and 11. It may, however, alternatively follow the assistmotor control routine shown in the flowchart of FIG. 18. In the lattercase, when there is a difference between the energy output from theengine 50 and the energy to be output to the drive shaft 22, forexample, while the engine 50 is being shifted to a new target drivingpoint with a significant change in accelerator pedal position AP, thebattery 94 is charged with the excess energy or the insufficient energyis discharged from the battery 94. Even in the transient period when theengine 50 has not yet reached the new target driving point with asignificant change in accelerator pedal position AP, this structureenables the torque set as the output torque command value Td*corresponding to the step-on amount of the accelerator pedal 64 to beoutput to the drive shaft 22.

In the structure of the power output apparatuses 20, 20A, and 20B of thefirst through the third embodiments discussed above, the clutch motor 30and the assist motor 40 are separately attached to the differentpositions of the drive shaft 22. Like a power output apparatus 20Cillustrated in FIG. 23 as a modification of the power output apparatus20, however, the clutch motor and the assist motor may be joinedintegrally with each other. A clutch motor 30C of the power outputapparatus 20C includes an inner rotor 34C connecting with the crankshaft56 and an outer rotor 32C linked with the drive shaft 22. Three-phasecoils 36C are attached to the inner rotor 34C, and permanent magnets 35Care set on the outer rotor 32C in such a manner that the outer surfaceand the inner surface thereof have different magnetic poles. An assistmotor 40C includes the outer rotor 32C of the clutch motor 30C and astator 43 with three-phase coils 44 mounted thereon. In this structure,the outer rotor 32C of the clutch motor 30C also works as the rotor ofthe assist motor 40C. Since the three-phase coils 36C are mounted on theinner rotor 34C linked with the crankshaft 56, the rotary transformer 38for supplying electric power to the three-phase coils 36C of the clutchmotor 30C is attached to the crankshaft 56.

In the power output apparatus 20C, the voltage applied to thethree-phase coils 36C on the inner rotor 34C is controlled against theinner-surface magnetic pole of the permanent magnets 35C set on theouter rotor 32C. This enables the clutch motor 30C to work in the samemanner as the clutch motor 30 of the power output apparatuses 20, 20A,and 20B of the first through the third embodiments having the clutchmotor 30 and the assist motor 40 separately attached to the drive shaft22. The voltage applied to the three-phase coils 44 on the stator 43 iscontrolled against the outer-surface magnetic pole of the permanentmagnets 35C set on the outer rotor 32C. This enables the assist motor40C to work in the same manner as the assist motor 40 of the poweroutput apparatus 20. All the operations of the power output apparatuses20, 20A, and 20B of the first through the third embodiments discussedabove are accordingly applicable to the power output apparatus 20C ofmodified structure. The operations include the torque control processbased on the routine of FIG. 5 or FIG. 16, the clutch motor controlprocess based on the routine of FIG. 8 or FIGS. 19 and 20, the assistmotor control process based on the routine of FIGS. 10 and 11 or FIG.18, and modifications thereof.

The outer rotor 32C functions concurrently as one of the rotors in theclutch motor 30C and as the rotor of the assist motor 40C, therebyeffectively reducing the size and weight of the power output apparatus20C.

The following describes another power output apparatus 20D as a fourthembodiment according to the present invention. FIG. 24 schematicallyillustrates structure of the power output apparatus 20D of the fourthembodiment. Referring to FIG. 24, the power output apparatus 20D of thefourth embodiment has a similar structure to that of the power outputapparatus 20 of the first embodiment, except that the assist motor 40 isattached to the crankshaft 56 placed between the engine 50 and theclutch motor 30. The same part as that of the power output apparatus 20of the first embodiment shown in FIG. 1, such as the controller 80, isthus omitted from the drawing of FIG. 24. The power output apparatus 20Dof the fourth embodiment can be mounted on the vehicle in the samemanner as shown in FIG. 3. The constituents of the power outputapparatus 20D of the fourth embodiment that are identical with those ofthe power output apparatus 20 of the first embodiment are expressed bylike numerals and not specifically described here. The numerals andsymbols used in the description of the first embodiment have the samemeanings in the fourth embodiment, unless otherwise specified.

The power output apparatus 20D of the fourth embodiment works in themanner discussed below. By way of example, it is assumed that the engine50 is driven at a driving point P1 (torque Te=T1 and revolving speedNe=N1) on the constant-output energy curve of FIG. 4 defined by thetorque and the revolving speed, and that the revolving speed Nd of thedrive shaft is equal to a value N2. When the assist motor 40 attached tothe crankshaft 56 applies a torque Ta (Ta=T2-T1) to the crankshaft 56,energy expressed as the sum of areas G2 and G3 in FIG. 4 is given to thecrankshaft 56, so that the torque on the crankshaft 56 becomes equal toa value T2 (=T1+Ta). When the torque Tc of the clutch motor 30B iscontrolled to have the value T2, the torque Tc (=T1+Ta) is transmittedto the drive shaft 22, while electric power based on the revolving speeddifference Nc between the revolving speed Ne of the engine 50 and therevolving speed Nd of the drive shaft Nd (that is, energy expressed bythe sum of areas G1 and G3) is regenerated by the clutch motor 30. Thetorque Ta of the assist motor 40 is then set to be just compensated bythe electric power regenerated by the clutch motor 30, and theregenerative power is supplied to the second driving circuit 92 via thepower lines L1 and L2, so that the assist motor 40 is driven with theregenerative power.

In accordance with another example, it is assumed that the engine 50 isdriven at a driving point P2 of FIG. 4 (torque Te=T2 and revolving speedNe=N2) and that the revolving speed Nd of the drive shaft 22 is equal tothe value N1. When the torque Ta of the assist motor 40 is controlled tohave the value (T2-T1), the assist motor 40 carries out the regenerativeoperation and regenerates energy (electric power) expressed by the areaG2 in FIG. 4 from the crankshaft 56. In the clutch motor 30, on theother hand, the inner rotor 34 rotates relative to the outer rotor 32 inthe direction of rotation of the drive shaft 22 at the revolving speeddifference Nc (=N1-N2). The clutch motor 30 accordingly functions as anormal motor and gives energy expressed by the area G1 corresponding tothe revolving speed difference Nc to the drive shaft 22 as the energy ofrotational motion. The torque Ta of the assist motor 40 is then set toenable the electric power consumed by the clutch motor 30 to be justcompensated by the electric power regenerated by the assist motor 40, sothat the clutch motor 30 is driven with the electric power regeneratedby the assist motor 40.

Like the power output apparatus 20 of the first embodiment, in the poweroutput apparatus 20D of the fourth embodiment, the torque Ta of theassist motor 40 and the torque Tc of the clutch motor 30 are controlledto hold Equations (15) and (16) given below. This enables the energyoutput from the engine 50 to be freely subjected to torque conversionand output to the drive shaft 22. The relations of Equations (15) and(16) represent an ideal state having the efficiency of 100%. In theactual state, Tc×Nd and Ta become a little smaller.

    Te×Ne=Tc×Nd                                    (15)

    Te+Ta=Tc                                                   (16)

The power output apparatus 20D of the fourth embodiment can execute thetorque control routine of FIG. 5, the clutch motor control routine ofFIG. 8, the assist motor control routine of FIGS. 10 and 11, thethrottle valve position control routine of FIG. 12, and the fuelinjection control routine of FIG. 13, which are carried out by the poweroutput apparatus 20 of the first embodiment. The power output apparatus20D can also execute the torque control routine of FIG. 16 carried outby the power output apparatus 20A of the second embodiment and theclutch motor control routine of FIGS. 19 and 20 carried out by the poweroutput apparatus 20B of the third embodiment. The power output apparatus20D can further execute the assist motor control routine of FIG. 18which may be carried out by the power output apparatus 20A of the secondembodiment or the power output apparatus 20B of the third embodiment.When the target torque Te* and the target revolving speed Ne* of theengine 50 are set at step S104 in the torque control routine of FIG. 5or at step S200 in the torque control routine of FIG. 16, the drivingpoint which attains the highest possible efficiency among the respectivedriving points on each constant-output energy curve of the engine 50 canbe set as the target driving point of the engine 50 as discussed abovewith the drawings of FIGS. 6 and 7.

The primary difference of the power output apparatus 20D of the fourthembodiment from the power output apparatuses 20 and 20A of the first andthe second embodiments is the arrangement of the clutch motor 30 and theassist motor 40. The difference in arrangement inverts the power controland regenerative control of the clutch motor 30 and the assist motor 40that are determined by the relationship between the revolving speed Neof the engine 50 and the revolving speed Nd of the drive shaft 22. Thisalso varies the setting of the torque command value Tc* of the clutchmotor 30 at step S113 in the clutch motor control routine of FIG. 8 andthe setting of the torque command value Ta* of the assist motor 40 atstep S136 or S138 in the assist motor control routine of FIG. 10. Whenneglecting the efficiency of the clutch motor 30 and the assist motor40, the power output apparatus 20D of the fourth embodiment candetermine the torque command value Tc* of the clutch motor 30 at stepS113 in the flowchart of FIG. 8 according to Equation (17) given below,instead of the above Equation (1), and determine the torque commandvalue Ta* of the assist motor 40 at steps S131 through S140 in theflowchart of FIG. 10 according to Equation (18) given below:

    Tc*=kc(Ne-Ne*)+Te*+Ta*                                     (17)

    Ta*=Td*-Tc*                                                (18)

The primary difference of the power output apparatus 20D of the fourthembodiment from the power output apparatus 20B of the third embodimentis also the arrangement of the clutch motor 30 and the assist motor 40.The difference in arrangement varies the calculation of the estimatedtorque Tef of the engine 50 at step S236 in the clutch motor controlroutine of FIG. 19 and the setting of the torque command value Tc* ofthe clutch motor 30 at step S240. The calculation of the estimatedtorque Tef of the engine 50 at step S236 follows Equation (19) givenbelow instead of the above Equation (13), whereas Equation (20) givenbelow is used instead of the above Equation (14) for the calculation ofthe torque command value Tc* of the clutch motor 30 at step S240.

    Tef=Tc+I×ω'-Ta                                 (19)

    Tc*=Tef+Ta+kc(Ne-Nef*)+∫ki(Ne-Nef*)dt                 (20)

As discussed above, the power output apparatus 20D of the fourthembodiment uses Equations (17) and (18) to implement the torque controlroutine of FIG. 5, the clutch motor control routine of FIG. 8, theassist motor control routine of FIGS. 10 and 11, and other relatedroutines carried out by the power output apparatus 20 of the firstembodiment. The torque Te and the revolving speed Ne at a specificdriving point, which attain the highest possible efficiency among therespective driving points on each constant-output energy curve of theengine 50, are set as the target engine torque Te* and the target enginespeed Ne*. This enhances the efficiency of the engine 50 and therebyimproves the efficiency of the whole power output apparatus 20D. Thedriving points set as the target engine torque Te* and the target enginespeed Ne* are continuous with respect to the amount of output energy.The driving point of the engine 50 can thus be shifted smoothly with alittle change in output energy Pd.

The power output apparatus 20D of the fourth embodiment can also executethe torque control routine of FIG. 16, which is carried out by the poweroutput apparatus 20A of the second embodiment. When the driver steps onthe accelerator pedal 64 by a relatively large amount, the power outputapparatus 20D controls the engine 50, the clutch motor 30, and theassist motor 40, based on the output energy at a driving point to whichthe engine 50 can smoothly shift from the current driving point, insteadof the output energy Pd corresponding to the step-on amount of theaccelerator pedal 64. This structure enables the driving point of theengine 50 to be smoothly shifted to the driving point giving the outputenergy Pd corresponding to the step-on amount of the accelerator pedal64, thereby effectively preventing the engine 50 from stalling orstopping due to an abrupt change of the driving point of the engine 50.

The power output apparatus 20D of the fourth embodiment uses Equations(19) and (20) to implement the torque control routine of FIG. 5 and theclutch motor control routine of FIGS. 19 and 20 carried out by the poweroutput apparatus 20B of the third embodiment. The power output apparatus20D estimates the torque currently output from the engine 50, andcontrols the torque Tc of the clutch motor 30 in order to enable theengine 50 to be driven at the driving point attaining the highestpossible efficiency with respect to the estimated torque. The engine 50can thus be driven at driving points of the highest possible efficiency.In case that the target driving point of the engine 50 is a fixedstationary state, the engine 50 is stably driven at the target drivingpoint. When the target driving point is changed, the engine 50 issmoothly shifted to the new target driving point along the path ofhigh-efficiency driving points. With a change of the target drivingpoint, the position BP of the throttle valve 66 is immediately varied toa value corresponding to the new target driving point, so that theengine 50 can be quickly shifted to the new target driving point.

The torque command value Tc* of the clutch motor 30 is set to lessen thedifference between the actual revolving speed Ne of the engine 50 andthe target engine speed Ne*. The engine 50 can thus be driven stably atthe target engine speed Ne*. The position BP of the throttle valve 66 isalso adjusted to decrease the difference between the revolving speed Neof the engine 50 and the target engine speed Ne*. This further ensuresstable operation of the engine 50 at the target engine speed Ne*.

In the power output apparatus 20D of the fourth embodiment shown in FIG.24, the assist motor 40 is attached to the crankshaft 56 placed betweenthe engine 50 and the clutch motor 30. Like another power outputapparatus 20E illustrated in FIG. 25, however, the engine 50 may beinterposed between the clutch motor 30 and the assist motor 40, both ofwhich are linked with the crankshaft 56.

One modification of the power output apparatus 20D of the fourthembodiment is given in FIG. 26 as a power output apparatus 20F, in whicha clutch motor 30F and an assist motor 40F are integrally joined witheach other. Referring to FIG. 26, in the power output apparatus 20F, anouter rotor 32F of the clutch motor 30F also works as a rotor of theassist motor 40F. The voltage applied to the three-phase coils 36 on theinner rotor 34 is controlled against the inner-surface magnetic pole ofpermanent magnets 35F set on the outer rotor 32F. This allows the clutchmotor 30F to work in the same manner as the clutch motor 30 of the poweroutput apparatus 20D shown in FIG. 24. The voltage applied to thethree-phase coils 44 on the stator 43 is controlled against theouter-surface magnetic pole of the permanent magnets 35F set on theouter rotor 32F. This allows the assist motor 40F to work in the samemanner as the assist motor 40 of the power output apparatus 20D. Thepower output apparatus 20F accordingly carries out the same operationsand exerts the same effects as those in the power output apparatus 20Dof the fourth embodiment discussed above. In addition to the effects ofthe power output apparatus 20D of the fourth embodiment, the poweroutput apparatus 20F of the modified structure has further effects ofreducing the size and weight of the whole power output apparatus 20F.

In the power output apparatuses 20 and 20A through 20F of the firstthrough the fourth embodiments and their modifications, the torque Teand the revolving speed Ne at a specific driving point, which attainsthe highest possible efficiency among the respective driving points oneach constant-output energy curve of the engine 50, are set as thetarget engine torque Te* and the target engine speed Ne*. The targettorque Te* and the target revolving speed Ne* of the engine 50 mayalternatively be set to allow the engine 50 as well as the clutch motor30 and the assist motor 40 to be driven at a driving point having thehighest possible comprehensive efficiency, which takes into account theefficiency of the clutch motor 30 and the assist motor 40 in addition tothe efficiency of the engine 50. By way of example, the efficiency ofthe engine 50 is given as ηe, the efficiency of the clutch motor 30 andthe first driving circuit 91 as ηc, and the efficiency of the assistmotor 40 and the second driving circuit 92 as ηa. A comprehensiveefficiency η is then expressed by multiplying the efficiency ηe of theengine 50 by an efficiency (transmission efficiency) of the power outputapparatus 20 for transmitting the power from the engine 50 to the driveshaft 22 as given by Equation (21) below. The driving points of theengine 50, the clutch motor 30, and the assist motor 40 attaining thehighest possible comprehensive efficiency η with respect to each amountof output energy Pd are determined experimentally or otherwise, andstored in advance as a map in the ROM 90b. The driving pointscorresponding to the output energy Pd, which depends upon the operationof the accelerator pedal 64, are read from the map. This structurefurther enhances the efficiency of the whole power output apparatus.##EQU3##

The following describes still another power output apparatus 110 as afifth embodiment according to the present invention. FIG. 27schematically illustrates structure of the power output apparatus 110 ofthe fifth embodiment; FIG. 28 is an enlarged view illustrating anessential part of the power output apparatus 110 of FIG. 27; and FIG. 29shows a vehicle with the power output apparatus 110 of FIG. 27incorporated therein.

The vehicle of FIG. 29 with the power output apparatus 110 of the fifthembodiment incorporated therein has a similar structure to that of thevehicle of FIG. 3 with the power output apparatus 20 of the firstembodiment incorporated therein, except that a planetary gear 120 andmotors MG1 and MG2 are attached to a crankshaft 156, instead of theclutch motor 30 and the assist motor 40. The same constituents areexpressed by like numerals +100 and not specifically described here. Thenumerals and symbols used in the description of the power outputapparatus 20 the first embodiment have the same meanings in thedescription of the power output apparatus 110 of the fifth embodiment,unless otherwise specified.

Referring to FIGS. 27 and 28, the power output apparatus 110 primarilyincludes an engine 150, a planetary gear 120 having a planetary carrier124 mechanically linked with a crankshaft 156 of the engine 150, a firstmotor MG1 linked with a sun gear 121 of the planetary gear 120, a secondmotor MG2 linked with a ring gear 122 of the planetary gear 120, and acontroller 180 for driving and controlling the first and the secondmotors MG1 and MG2.

The planetary gear 120 includes the sun gear 121 linked with a hollowsun gear shaft 125 which the crankshaft 156 passes through, the ringgear 122 linked with a ring gear shaft 126 coaxial with the crankshaft156, a plurality of planetary pinion gears 123 arranged between the sungear 121 and the ring gear 122 to revolve around the sun gear 121 whilerotating on its axis, and the planetary carrier 124 connecting with oneend of the crankshaft 156 to support the rotating shafts of theplanetary pinion gears 123. In the planetary gear 120, three shafts,that is, the sun gear shaft 125, the ring gear shaft 126, and thecrankshaft 156 respectively connecting with the sun gear 121, the ringgear 122, and the planetary carrier 124, work as input and output shaftsof the power. Determination of the power input to or output from any twoshafts among the three shafts automatically determines the power inputto or output from the residual one shaft. The details of the input andoutput operations of the power into or from the three shafts of theplanetary gear 120 will be discussed later.

A power feed gear 128 for taking out the power is linked with the ringgear 122 and arranged on the side of the first motor MG1. The power feedgear 128 is further connected to a power transmission gear 111 via achain belt 129, so that the power is transmitted between the power feedgear 128 and the power transmission gear 111. As shown in FIG. 29, thepower transmission gear 111 is further linked with a differential gear114. The power output from the power output apparatus 110 is thuseventually transmitted to left and right driving wheels 116 and 118.

The first motor MG1 is constructed as a synchronous motor-generatorgenerator and includes a rotor 132 having a plurality of permanentmagnets 135 on its outer surface and a stator 133 having three-phasecoils 134 wound thereon to form a revolving magnetic field. The rotor132 is linked with the sun gear shaft 125 connecting with the sun gear121 of the planetary gear 120. The stator 133 is prepared by laying thinplates of non-directional electromagnetic steel one upon another and isfixed to a casing 119. The first motor MG1 works as a motor for rotatingthe rotor 132 through the interaction between a magnetic field producedby the permanent magnets 135 and a magnetic field produced by thethree-phase coils 134, or as a generator for generating an electromotiveforce on either ends of the three-phase coils 134 through theinteraction between the magnetic field produced by the permanent magnets135 and the rotation of the rotor 132. The sun gear shaft 125 is furtherprovided with a resolver 139 for measuring its rotational angle θs.

Like the first motor MG1, the second motor MG2 is also constructed as asynchronous motor-generator and includes a rotor 142 having a pluralityof permanent magnets 145 on its outer surface and a stator 143 havingthree-phase coils 144 wound thereon to form a revolving magnetic field.The rotor 142 is linked with the ring gear shaft 126 connecting with thering gear 122 of the planetary gear 120, whereas the stator 14 is fixedto the casing 119. The stator 143 of the motor MG2 is also produced bylaying thin plates of non-directional electromagnetic steel one uponanother. Like the first motor MG1, the second motor MG2 also works as amotor or a generator. The ring gear shaft 126 is further provided with aresolver 149 for measuring its rotational angle θr.

Referring to FIG. 27, the controller 180 incorporated in the poweroutput apparatus 110 of the fifth embodiment is constructed in the samemanner as the controller 80 of the power output apparatus 20 of thefirst embodiment. The controller 180 includes a first driving circuit191 for driving the first motor MG1, a second driving circuit 192 fordriving the second motor MG2, a control CPU 190 for controlling both thefirst and the second driving circuits 191 and 192, and a battery 194including a number of secondary cells. The control CPU 190 furtherincludes a RAM 190a used as a working memory, a ROM 190b in whichvarious control programs are stored, an input/output port (not shown),and a serial communication port (not shown) through which data are sentto and received from an EFIECU 170. The control CPU 190 receives avariety of data via the input port. The input data include therotational angle θs of the sun gear shaft 125 measured with the resolver139, the rotational angle θr of the ring gear shaft 126 measured withthe resolver 149, an accelerator pedal position AP output from anaccelerator position sensor 165, a gearshift position SP output from agearshift position sensor 184, currents Iu1 and Iv1 from two ammeters195 and 196 disposed in the first driving circuit 191, currents Iu2 andIv2 from two ammeters 197 and 198 disposed in the second driving circuit192, and a remaining charge BRM of the battery 194 measured with aremaining charge meter 199.

The control CPU 190 outputs a first control signal SW1 for driving sixtransistors Tr1 through Tr6 working as switching elements of the firstdriving circuit 191 and a second control signal SW2 for driving sixtransistors Tr11 through Tr16 working as switching elements of thesecond driving circuit 192. The six transistors Tr1 through Tr6 in thefirst driving circuit 191 constitute a transistor inverter and arearranged in pairs to work as a source and a drain with respect to a pairof power lines L1 and L2. The six transistors Tr11 through Tr16 in thesecond driving circuit 192 also constitute a transistor inverter and arearranged in the same manner. The three-phase coils 134 of the firstmotor MG1 are connected to the respective contacts of the pairedtransistors in the first driving circuit 191, whereas the three-phasecoils 144 of the second motor MG2 are connected to those in the seconddriving circuit 192. The power lines L1 and L2 are respectivelyconnected to plus and minus terminals of the battery 194. The controlsignals SW1 and SW2 output from the control CPU 190 thus successivelycontrol the power-on time of the paired transistors Tr1 through Tr6 andthe paired transistors Tr11 through Tr16. The electric currents flowingthrough the three-phase coils 134 and 144 undergo PWM (pulse widthmodulation) to give quasi-sine waves, which enable the three-phase coils134 and 144 to form revolving magnetic fields.

The power output apparatus 110 of the fifth embodiment thus constructedworks in accordance with the operation principles discussed below,especially with the principle of torque conversion. By way of example,it is assumed that the engine 150 is driven at a driving point P1 havingthe revolving speed Ne and the torque Te and that the ring gear shaft126 is driven at another driving point P2 having different revolvingspeed Nr and torque Tr but the same energy as an energy Pe output fromthe engine 150. This means that the power output from the engine 150 issubjected to torque conversion and applied to the ring gear shaft 126.The relationship between the torque and the revolving speed of theengine 150 and the ring gear shaft 126 under such conditions is shown inthe graph of FIG. 4.

According to the mechanics, the relationship between the revolving speedand the torque of the three shafts in the planetary gear 120 (that is,the sun gear shaft 125, the ring gear shaft 126, and the planetarycarrier 124) can be expressed as nomograms illustrated in FIGS. 30 and31 and solved geometrically. The relationship between the revolvingspeed and the torque of the three shafts in the planetary gear 120 maybe analyzed numerically through calculation of energies of therespective shafts, without using the nomograms. For the clarity ofexplanation, the nomograms are used in the fifth embodiment.

In the graph of FIG. 30, the revolving speed of the three shafts isplotted as ordinate and the positional ratio of the coordinate axes ofthe three shafts as abscissa. When a coordinate axis S of the sun gearshaft 125 and a coordinate axis R of the ring gear shaft 126 arepositioned on either ends of a line segment, a coordinate axis C of theplanetary carrier 124 is given as an interior division of the axes S andR at the ratio of 1 to ρ, where ρ represents a ratio of the number ofteeth of the ring gear 122 to that of the sun gear 121 and expressed asEquation (22) given below: ##EQU4##

As mentioned above, the engine 150 is driven at the revolving speed Ne,while the ring gear shaft 126 is driven at the revolving speed Nr. Therevolving speed Ne of the engine 150 can thus be plotted on thecoordinate axis C of the planetary carrier 124 linked with thecrankshaft 156 of the engine 150, and the revolving speed Nr of the ringgear shaft 126 on the coordinate axis R of the ring gear shaft 126. Astraight line passing through both the points is drawn, and a revolvingspeed Ns of the sun gear shaft 125 is then given as the intersection ofthis straight line and the coordinate axis S. This straight line ishereinafter referred to as dynamic collinear line. The revolving speedNs of the sun gear shaft 125 can be calculated from the revolving speedNe of the engine 150 and the revolving speed Nr of the ring gear shaft126 according to a proportional expression given as Equation (23) below.In the planetary gear 120, the determination of the rotations of any twoshafts among the sun gear 121, the ring gear 122, and the planetarycarrier 124 results in automatically setting the rotation of theresidual one shaft. ##EQU5##

The torque Te of the engine 150 is then applied (upward in the drawing)to the dynamic collinear line at the coordinate axis C of the planetarycarrier 124 as a line of action. The dynamic collinear line against thetorque can be handled as a rigid body to which a force is applied as avector. Based on the technique of dividing the force into differentlines of action having the same direction, the torque Te acting on thecoordinate axis C is divided into a torque Tes on the coordinate axis Sand a torque Ter on the coordinate axis R. The magnitudes of the torquesTes and Ter are given by Equations (24) and (25) below: ##EQU6##

The equilibrium of forces on the dynamic collinear line is essential forthe stable state of the dynamic collinear line. In accordance with aconcrete procedure, a torque Tm1 having the same magnitude as but theopposite direction to the torque Tes is applied to the coordinate axisS, whereas a torque Tm2 having the same magnitude as but the oppositedirection to a resultant force of the torque Ter and the torque that hasthe same magnitude as but the opposite direction to the torque Tr outputto the ring gear shaft 126 is applied to the coordinate axis R. Thetorque Tm1 is given by the first motor MG1, and the torque Tm2 by thesecond motor MG2. The first motor MG1 applies the torque Tm1 in reverseof its rotation and thereby works as a generator to regenerate anelectrical energy Pm1, which is given as the product of the torque Tm1and the revolving speed Ns, from the sun gear shaft 125. The secondmotor MG2 applies the torque Tm2 in the direction of its rotation andthereby works as a motor to output an electrical energy or power Pm2,which is given as the product of the torque Tm2 and the revolving speedNr, to the ring gear shaft 126.

In case that the electrical energy Pm1 is identical with the electricalenergy Pm2, all the electric power consumed by the second motor MG2 canbe supplied by the electric power regenerated by the first motor MG1. Inorder to attain such a state, all the input energy should be output;that is, the energy Pe output from the engine 150 should be equal to anenergy Pr output to the ring gear shaft 126. Namely the energy Peexpressed as the product of the torque Te and the revolving speed Ne ismade equal to the energy Pr expressed as the product of the torque Trand the revolving speed Nr. Referring to FIG. 4, the power that isexpressed as the product of the torque Te and the revolving speed Ne andoutput from the engine 150 driven at the driving point P1 is subjectedto torque conversion and output to the ring gear shaft 126 as the powerof the same energy but expressed as the product of the torque Tr and therevolving speed Nr. As discussed previously, the power output to thering gear shaft 126 is transmitted to a drive shaft 112 via the powerfeed gear 128 and the power transmission gear 111, and furthertransmitted to the driving wheels 116 and 118 via the differential gear114. A linear relationship is accordingly held between the power outputto the ring gear shaft 126 and the power transmitted to the drivingwheels 116 and 118. The power transmitted to the driving wheels 116 and118 can thus be controlled by adjusting the power output to the ringgear shaft 126.

Although the revolving speed Ns of the sun gear shaft 125 is positive inthe nomogram of FIG. 30, it may be negative according to the revolvingspeed Ne of the engine 150 and the revolving speed Nr of the ring gearshaft 126 as shown in the nomogram of FIG. 31. In the latter case, thefirst motor MG1 applies the torque in the direction of its rotation andthereby works as a motor to consume the electrical energy Pm1 given asthe product of the torque Tm1 and the revolving speed Ns. The secondmotor MG2, on the other hand, applies the torque in reverse of itsrotation and thereby works as a generator to regenerate the electricalenergy Pm2, which is given as the product of the torque Tm2 and therevolving speed Nr, from the ring gear shaft 126. In case that theelectrical energy Pm1 consumed by the first motor MG1 is made equal tothe electrical energy Pm2 regenerated by the second motor MG2 under suchconditions, all the electric power consumed by the first motor MG1 canbe supplied by the electric power regenerated by the second motor MG2.

The operation principle discussed above is on the assumption that theefficiency of power conversion by the planetary gear 120, the motors MG1and MG2, and the transistors Tr1 through Tr16 is equal to the value `1`,which represents 100%. In the actual state, however, the conversionefficiency is less than the value `1`, so that the energy Pe output fromthe engine 150 should be a little greater than the energy Pr output tothe ring gear shaft 126 or alternatively the energy Pr output to thering gear shaft 126 should be a little smaller than the energy Pe outputfrom the engine 150. By way of example, the energy Pe output from theengine 150 may be calculated by multiplying the energy Pr output to thering gear shaft 126 by the reciprocal of the conversion efficiency. Inthe state of the nomogram of FIG. 30, the torque Tm2 of the second motorMG2 is calculated by multiplying the electric power regenerated by thefirst motor MG1 by the efficiencies of both the motors MG1 and MG2. Inthe state of the nomogram of FIG. 31, on the other hand, the torque Tm2of the second motor MG2 is calculated by dividing the electric powerconsumed by the first motor MG1 by the efficiencies of both the motorsMG1 and MG2. In the planetary gear 120, there is an energy loss or heatloss due to a mechanical friction or the like, though the amount ofenergy loss is significantly smaller than the whole amount of energyconcerned. The efficiency of the synchronous motors used for the firstand the second motors MG1 and MG2 is substantially equal to the value`1`. Known devices such as GTOs applicable to the transistors Tr1through Tr16 have extremely small ON-resistance. The efficiency of powerconversion thus becomes practically equal to the value `1`. For thematter of convenience, in the following discussion of the fifthembodiment, the efficiency is assumed to be equal to the value `1`(=100%) unless otherwise specified.

As clearly understood from the operation principle of the power outputapparatus 110 of the fifth embodiment discussed above, controlling themotors MG1 and MG2 enables the engine 150 to be driven at any drivingpoint that can output the energy identical with the energy to be outputto the ring gear shaft 126. The planetary gear 120 (having theappropriate gear ratio) and the first motor MG1 in the power outputapparatus 110 of the fifth embodiment have similar functions to those ofthe clutch motor 30 in the power output apparatus 20 of the firstembodiment, while the second motor MG2 works in the similar manner tothe assist motor 40. The map of FIG. 6, which is used to set the targettorque Te* and the target revolving speed Ne* of the engine 50 in thetorque control of the power output apparatuses 20 and 20A through 20C ofthe first through the third embodiments, can thus be applicable to setthe target torque Te* and the target revolving speed Ne* of the engine150 in the torque control of the power output apparatus 110 of the fifthembodiment.

By taking into account the gear ratio of the planetary gear 120, thepower output apparatus 110 of the fifth embodiment can execute thetorque control routine of FIG. 5, the clutch motor control routine ofFIG. 8, the assist motor control routine of FIGS. 10 and 11, thethrottle valve position control routine of FIG. 12, and the fuelinjection control routine of FIG. 13, which are carried out by the poweroutput apparatus 20 of the first embodiment. The power output apparatus110 can also execute the torque control routine of FIG. 16 carried outby the power output apparatus 20A of the second embodiment and theclutch motor control routine of FIGS. 19 and 20 carried out by the poweroutput apparatus 20B of the third embodiment. The power output apparatus110 can further execute the assist motor control routine of FIG. 18which may be carried out by the power output apparatus 20A of the secondembodiment or the power output apparatus 20B of the third embodiment.The following describes a typical operation of the power outputapparatus 110 of the fifth embodiment, which is similar to that of thepower output apparatus 20B of the third embodiment.

The torque control in the power output apparatus 110 of the fifthembodiment is carried out according to a torque control routine shown inthe flowchart of FIG. 32. When the program enters the torque controlroutine, the control CPU 190 of the controller 180 first reads therevolving speed Nr of the ring gear shaft 126 at step S300. Therevolving speed Nr of the ring gear shaft 126 may be calculated from therotational angle θr of the ring gear shaft 126 read from the resolver149. The control CPU 190 then reads the accelerator pedal position APdetected by the accelerator position sensor 165 at step S302, anddetermines a torque command value Tr* or a target torque to be output tothe ring gear shaft 126, based on the input accelerator pedal positionAP at step S304. Not the torque to be output to the driving wheels 116and 118 but the torque to be output to the ring gear shaft 126 iscalculated here from the accelerator pedal position AP. This is becausethe ring gear shaft 126 is mechanically linked with the driving wheels116 and 118 via the power feed gear 128, the power transmission gearl11, and the differential gear 114 and the determination of the torqueto be output to the ring gear shaft 126 thus results in determining thetorque to be output to the driving wheels 116 and 118. In the fifthembodiment, a map representing the relationship between the torquecommand value Tr*, the revolving speed Nr of the ring gear shaft 126,and the accelerator pedal position AP is prepared in advance and storedin the ROM 190b. The torque command value Tr* corresponding to the inputaccelerator pedal position AP and the input revolving speed Nr of thering gear shaft 126 is read from the map.

The control CPU 190 subsequently calculates an energy Pr to be output tothe ring gear shaft 126 from the torque command value Tr* thus obtainedand the input revolving speed Nr of the ring gear shaft 126 (Pr=Tr*×Nr)at step S306. The program then proceeds to step S308 to set a targettorque Te* and a target revolving speed Ne* of the engine 150 based onthe energy Pr to be output to the ring gear shaft 126. As mentionedabove, the map of FIG. 6 used in the power output apparatus 20 of thefirst embodiment is applicable to set the target torque Te* and thetarget revolving speed Ne* of the engine 150. The map of FIG. 6 enablesa specific driving point of the engine 150 that attains the highestpossible efficiency with respect to each amount of energy Pr and allowsa smooth variation in driving state of the engine 150 with a variationin energy Pr to be set as the target engine torque Te* and the targetengine speed Ne*.

After setting the target torque Te* and the target revolving speed Ne*of the engine 150, the program proceeds to steps S310, S312, and S314 torespectively control the first motor MG1, the second motor MG2, and theengine 150 based on the target engine torque Te* and the target enginespeed Ne* thus obtained. In the fifth embodiment, although the controloperations of the first motor MG1, the second motor MG2, and the engine150 are shown as separate steps for the matter of convenience, thesecontrols are carried out simultaneously in the actual procedure.

FIGS. 33 and 34 are flowcharts showing details of the control process ofthe first motor MG1 executed at step S310 in the flowchart of FIG. 32.When the program enters the control routine, the control CPU 190 of thecontroller 180 first reads the torque Tm1 which the first motor MG1currently applies to the sun gear shaft 125 (that is, a torque commandvalue Tm1* currently set in the first motor MG1) at step S320, andreceives data of revolving speed Ns of the sun gear shaft 125 at stepS322. The revolving speed Ns of the sun gear shaft 125 can be calculatedfrom the rotational angle θs of the sun gear shaft 125 read from theresolver 139. At subsequent step S324, a change rate ωs' of rotationalspeed of the sun gear shaft 125 is calculated from the input revolvingspeed Ns of the sun gear shaft 125 according to Equation (26) givenbelow. The calculation subtracts previous data of revolving speed NS ofthe sun gear shaft 125 (previous NS) input at step S322 in a previouscycle of this routine from the current data of revolving speed NS,multiplies the difference by 2π, and divides the product by an intervalΔt of activating this routine, so as to determine the change rate ωs' ofrotational speed of the sun gear shaft 125. The numerator in the rightside of Equation (26) includes `2π` since the relationship between therotational speed ωs and the revolving speed Ns of the sun gear shaft 125is defined as ωs=2π×Ns [rad/sec]. Like the third embodiment, thisroutine of the fifth embodiment can be normally executed evenimmediately after a start of the vehicle, since the previous Ns isinitialized to zero in an initialization routine (not shown) executedprior to this routine. ##EQU7##

The control CPU 190 then reads the revolving speed Nr of the ring gearshaft 126 at step S326, and calculates a change rate ωr' of rotationalspeed of the ring gear shaft 126 at step S328 in a similar manner to theprocessing of step S324. After calculating the change rate ωs' ofrotational speed of the sun gear shaft 125 and the change rate ωr' ofrotational speed of the ring gear shaft 126, the program proceeds tostep S330 to calculate an estimated torque Tef, which the engine 150 isassumed to currently output, according to Equation (27) given below:##EQU8## wherein `Ie` in the right side of Equation (27) represents themoment of inertia around the engine 150 and the crankshaft 156, and `Ig`represents the moment of inertia around the rotor 132 of the first motorMG1 and the sun gear shaft 125. Equation (27) is led from the equationof motion based on the equilibrium of forces on the dynamic collinearline in the nomograms of FIGS. 30 and 31.

At subsequent step S332, the control CPU 190 reads a revolving speed(estimated target revolving speed) Nef* corresponding to the estimatedtorque Tef of the engine 150 from the map of FIG. 6 for determining thedriving point of the engine 150. Like the third embodiment, for example,as shown in FIG. 21, the estimated target revolving speed Nef* isdetermined as a value corresponding to the estimated torque Tef on thecurve A of driving points attaining the highest possible efficiency ofthe engine 150. A target revolving speed Ns* of the sun gear shaft 125is then calculated at step S334 from the estimated target revolvingspeed Nef* thus obtained and the input revolving speed Nr of the ringgear shaft 126 according to Equation (28) given below: ##EQU9## Equation(28) is readily obtained by calculating the ratio of revolving speeds ofthe respective coordinate axes S, C, and R in the nomograms of FIGS. 30and 31.

At subsequent step S336, the control CPU 190 calculates a torque commandvalue Tm1* of the first motor MG1 from the estimated torque Tef, theestimated target revolving speed Nef*, and the target revolving speedNs* of the sun gear shaft 125 according to Equation (29) given below:##EQU10## The second term in the right side of Equation (29) representsa correction term based on the difference between the actual revolvingspeed Ns of the sun gear shaft 125 and the target revolving speed Ns*,wherein ke denotes a constant. The third term in the right side ofEquation (29) represents an integral term to cancel the stationarydeviation of the revolving speed Ns of the sun gear shaft 125 from thetarget revolving speed Ns*, wherein ki denotes a constant. The firstmotor MG1 is controlled with the torque command value Tm1* of the firstmotor MG1 thus obtained, so that the engine 150 is controlled to bedriven at a specific driving point where the torque Te is equal to theestimated torque Tef and the revolving speed Ne is equal to theestimated target revolving speed Nef*.

The engine 150 can be driven at the specific driving point of theestimated toque Tef and the estimated target revolving speed Nef* bycontrolling the revolving speed Ns of the sun gear shaft 125 to thetarget revolving speed Ns*. This is ascribed to the following reasons.As discussed above with the nomograms of FIGS. 30 and 31, in theplanetary gear 120, the determination of the revolving speeds of any twoshafts among the sun gear shaft 125, the ring gear shaft 126, and theplanetary carrier 124 results in automatically setting the revolvingspeed of the residual one shaft. The revolving speed Nr of the ring gearshaft 126 mechanically linked with the driving wheels 116 and 118 isgiven as input data. Controlling either the revolving speed Ns of thesun gear shaft 125 or the revolving speed Ne of the engine 150 thusdetermines the rotational conditions of the three shafts in theplanetary gear 120. The revolving speed Ne of the engine 150 should becontrolled, in order to allow the engine 150 to be driven at thehigh-efficient driving point of the estimated torque Tef and theestimated target revolving speed Nef*. The torque Te and the revolvingspeed Ne of the engine 150 are, however, varied by the loading torque ofthe engine 150, even when the position BP of the throttle valve 166 andthe amount of fuel injection are adjusted finely. It is thereby ratherdifficult to control the driving point of the engine 150 in anindependent manner. The revolving speed Ns of the sun gear shaft 125can, on the other hand, be controlled readily and precisely bycontrolling the revolving speed of the first motor MG1. In the fifthembodiment, the control of the revolving speed Ne of the engine 150 isthus implemented by controlling the revolving speed Ns of the sun gearshaft 125 with the first motor MG1.

Referring to the flowchart of FIG. 34, the control CPU 190 subsequentlyreceives the rotational angle θs of the sun gear shaft 125 from therevolver 139 at step S338, and detects phase currents Iu1 and Iv1 of thefirst motor MG1 with the ammeters 195 and 196 at step S340. The controlCPU 190 then executes transformation of coordinates for the phasecurrents at step S342, computes voltage command values Vd1 and Vq1 atstep S344, and executes inverse transformation of coordinates for thevoltage command values at step S346. At subsequent step S348, thecontrol CPU 190 determines the on- and off-time of the transistors Tr1through Tr6 in the first driving circuit 191 of the controller 180 fordriving and controlling the first motor MG1 and carries out the PWM(pulse width modulation) control. The processing executed at steps S342through S348 is similar to that executed at steps S120 through S126 inthe clutch motor control routine of the first embodiment shown in theflowchart of FIG. 8.

FIG. 35 is a flowchart showing details of the control process of thesecond motor MG2 executed at step S312 in the flowchart of FIG. 32. Whenthe program enters the control routine, the control CPU 190 of thecontroller 180 first calculates a torque command value Tm2* of thesecond motor MG2 according to Equation (30) given below at step S350.Equation (30) gives the torque command value Tm2* of the second motorMG2, in order to enable all the power output from the engine 150 to besubjected to torque conversion by the planetary gear 120 and the motorsMG1 and MG2 and to be output to the ring gear shaft 126. This is on theassumption that, when the engine 150 is driven at a specific drivingpoint defined by the estimated torque Tef and the estimated targetrevolving speed Nef*, the dynamic collinear line in the nomogram iswell-balanced. ##EQU11##

The control CPU 190 subsequently receives the rotational angle θr of thering gear shaft 126 from the revolver 149 at step S352, and detectsphase currents Iu2 and Iv2 of the second motor MG2 with the ammeters 197and 198 at step S354. The control CPU 190 then executes transformationof coordinates for the phase currents at step S356, computes voltagecommand values Vd2 and Vq2 at step S358, and executes inversetransformation of coordinates for the voltage command values at stepS360. At subsequent step S362, the control CPU 190 determines the on-and off-time of the transistors Tr11 through Tr16 in the second drivingcircuit 192 of the controller 180 for driving and controlling the secondmotor MG2 and carries out the PWM control. The processing executed atsteps S356 through S362 is similar to that executed at steps S342through S348 in the control procedure of the first motor MG1 illustratedin the flowcharts of FIGS. 33 and 34.

As discussed above, the power output apparatus 110 of the fifthembodiment estimates the torque currently output from the engine 150,and controls the torque Tm1 of the first motor MG1 in order to enablethe engine 150 to be driven at the driving point attaining the highestpossible efficiency with respect to the estimated torque. The engine 150can thus be driven at driving points of the highest possible efficiency.In case that the target driving point of the engine 150 is a fixedstationary state, the engine 150 is stably driven at the target drivingpoint. When the target driving point is changed, the engine 150 issmoothly shifted to the new target driving point along the path ofhigh-efficiency driving points. With a change of the target drivingpoint, the position BP of the throttle valve 166 is immediately variedto a value corresponding to the new target driving point, so that theengine 150 can be quickly shifted to the new target driving point.

The power output apparatus 110 of the fifth embodiment sets the torqueTe and the revolving speed Ne at a specific driving point, which attainsthe highest possible efficiency among the respective driving points oneach constant-output energy curve of the engine 150, as the targetengine torque Te* and the target engine speed Ne*. This further enhancesthe operation efficiency of the engine 150 and thereby improves theefficiency of the whole power output apparatus 110.

A variety of processes applied to the hardware structures of the poweroutput apparatuses 20, 20A, and 20B of the first through the thirdembodiments including the clutch motor 30 and the assist motor 40 arealso applicable to the hardware structure of the power output apparatus110 of the fifth embodiment including the planetary gear 120 and the twomotors MG1 and MG2 instead of the clutch motor 30 and the assist motor40, by taking into account the balance on the dynamic collinear line inthe nomograms of FIGS. 30 and 31. The processes carried out by the poweroutput apparatus 20B of the third embodiment are discussed above as anexample of the applicable processes. By taking into account the balanceon the dynamic collinear line in the nomograms of FIGS. 30 and 31, anyprocesses carried out by the power output apparatus 20 of the firstembodiment are also applicable to the power output apparatus 110 of thefifth embodiment, which thereby implements the same functions and exertsthe same effects as those of the first embodiment. In the same manner,by taking into account the balance on the dynamic collinear line in thenomograms of FIGS. 30 and 31, any processes carried out by the poweroutput apparatus 20A of the second embodiment are also applicable to thepower output apparatus 110 of the fifth embodiment, which therebyimplements the same functions and exerts the same effects as those ofthe second embodiment.

In the power output apparatus 110 of the fifth embodiment, the poweroutput to the ring gear shaft 126 is taken out of the place between thefirst motor MG1 and the second motor MG2 via the power feed gear 128connecting with the ring gear 122. As shown by another power outputapparatus 110A of FIG. 36 given as a possible modification, however, thepower may be taken out of the casing 119, from which the ring gear shaft126 is extended. FIG. 37 shows still another power output apparatus 110Bas another possible modification, wherein the engine 150, the planetarygear 120, the second motor MG2, and the first motor MG1 are arranged inthis order. In this case, a sun gear shaft 125B may not have a hollowstructure, whereas a hollow ring gear shaft 126B is required. Thismodified structure enables the power output to the ring gear shaft 126Bto be taken out of the place between the engine 150 and the second motorMG2.

The following describes still another power output apparatus 110C as asixth embodiment according to the present invention. FIG. 38 shows anessential part of the power output apparatus 110C of the sixthembodiment. Referring to FIG. 38, the power output apparatus 110C of thesixth embodiment has a similar structure to that of the power outputapparatus 110 of the fifth embodiment, except that the rotor 142 of thesecond motor MG2 is attached to the crankshaft 156 and that the twomotors MG1 and MG2 have a different arrangement. The same part as thatof the power output apparatus 110 of the fifth embodiment shown in FIG.27, such as the controller 180, is thus omitted from the drawing of FIG.38. The power output apparatus 110C of the sixth embodiment can bemounted on the vehicle in the same manner as shown in FIG. 29. Theconstituents of the power output apparatus 110C of the sixth embodimentthat are identical with those of the power output apparatus 110 of thefifth embodiment are expressed by like numerals and not specificallydescribed here. The numerals and symbols used in the description of thefifth embodiment have the same meanings in the sixth embodiment, unlessotherwise specified.

Referring to FIG. 38, in the power output apparatus 110C of the sixthembodiment, the engine 150, the second motor MG2, the planetary gear120, and the first motor MG1 are arranged in this order. The rotor 132of the first motor MG1 is attached to a sun gear shaft 125C connectingwith the sun gear 121 of the planetary gear 120. Like the power outputapparatus 110 of the fifth embodiment, the planetary carrier 124 isattached to the crankshaft 156 of the engine 150. The rotor 142 of thesecond motor MG2 and a resolver 157 for detecting a rotational angle θeof the crankshaft 156 are further attached to the crankshaft 156. A ringgear shaft 126C linked with the ring gear 122 of the planetary gear 120has another resolver 149 mounted thereon for detecting a rotationalangle θr of the ring gear shaft 126C and is connected to the power feedgear 128.

The arrangement of the power output apparatus 110C of the sixthembodiment is different from that of the power output apparatus 110 ofthe fifth embodiment. In both the arrangements, however, the three-phasecoils 134 of the first motor MG1 are connected with the first drivingcircuit 191 of the controller 180, and the three-phase coils 144 of thesecond motor MG2 with the second driving circuit 191. Although not beingillustrated, the resolver 157 is connected to the input port of thecontrol CPU 190 of the controller 180 via a signal line.

The power output apparatus 110C of the sixth embodiment works in themanner discussed below. By way of example, it is assumed that the engine150 is driven at the driving point P1 of the revolving speed Ne and thetorque Te and that the ring gear shaft 126C is driven at the drivingpoint P2 that is defined by the revolving speed Nr and the torque Tr andgives energy Pr (Pr=Nr×Tr) identical with energy Pe (Pe=Ne×Te) outputfrom the engine 150. In this example, the power output from the engine150 is thereby subjected to torque conversion and applied to the ringgear shaft 126C. FIGS. 39 and 40 are nomograms under such conditions.

Equations (31) through (34) given below are led by taking into accountthe balance on a dynamic collinear line in the nomogram of FIG. 39.Equation (31) is derived from the balance between the energy Pe inputfrom the engine 150 and the energy Pr output to the ring gear shaft126C. Equation (32) is given as a sum of energy input into the planetarycarrier 124 via the crankshaft 156. Equations (33) and (34) are obtainedby dividing the torque acting on the planetary carrier 124 into torqueson the coordinate axes S and R working as lines of action. ##EQU12##

The equilibrium of forces on the dynamic collinear line is essential forthe stable state of the dynamic collinear line. For that purpose, thetorque Tm1 should be made equal to a torque Tcs, and the torque Tr equalto a torque Tcr. Based on such relations, the torques Tm1 and Tm2 areexpressed as Equations (35) and (36) given below:

    Tm1=Tr×ρ                                         (35)

    Tm2=Tr×(1+ρ)-Te                                  (36)

The first motor MG1 applies the torque Tm1 determined by Equation (35)to the sun gear shaft 125C, while the second motor MG2 applies thetorque Tm2 determined by Equation (36) to the crankshaft 156. Thisenables the power output from the engine 150 and defined by the torqueTe and the revolving speed Ne to be converted to the power defined bythe torque Tr and revolving speed Nr and output to the ring gear shaft126. Under the condition of the nomogram of FIG. 39 the first motor MG1applies the torque in reverse of the rotation of the rotor 132 andthereby functions as a generator to regenerate electrical energy Pm1expressed as the product of the torque Tm1 and the revolving speed Ns.The second motor MG2, on the other hand, applies the torque in thedirection of rotation of the rotor 142 and thereby functions as a motorto consume electrical energy Pm2 expressed as the product of the torqueTm2 and the revolving speed Nr.

Although the revolving speed Ns of the sun gear shaft 125C is positivein the nomogram of FIG. 39, it may be negative according to therevolving speed Ne of the engine 150 and the revolving speed Nr of thering gear shaft 126C as shown in the nomogram of FIG. 40. In the lattercase, the first motor MG1 applies the torque in the direction ofrotation of the rotor 132 and thereby functions as a motor to consumethe electrical energy Pm1 expressed as the product of the torque Tm1 andthe revolving speed Ns. The second motor MG2, on the other hand, appliesthe torque in reverse of the rotation of the rotor 142 and therebyfunctions as a generator to regenerate the electrical energy Pm2, whichis expressed as the product of the torque Tm2 and the revolving speedNr, from the ring gear shaft 126C.

Like the power output apparatus 110 of the fifth embodiment, theoperation principle of the power output apparatus 110C of the sixembodiment discussed above is on the assumption that the efficiency ofpower conversion by the planetary gear 120, the motors MG1 and MG2, andthe transistors Tr1 through Tr16 is equal to the value `1`, whichrepresents 100%. In the actual state, however, the conversion efficiencyis less than the value `1`, so that the energy Pe output from the engine150 should be a little greater than the energy Pr output to the ringgear shaft 126C or alternatively the energy Pr output to the ring gearshaft 126C should be a little smaller than the energy Pe output from theengine 150. As discussed previously, an energy loss in the planetarygear 120 due to a mechanical friction or the like is significantly smalland the efficiency of the synchronous motors used for the first and thesecond motors MG1 and MG2 is substantially equal to the value `1`. Theefficiency of power conversion thus becomes practically equal to thevalue `1`. In the following discussion of the sixth embodiment, theefficiency is assumed to be equal to the value `1` (=100%) unlessotherwise specified.

As clearly understood from the operation principle of the power outputapparatus 110C of the sixth embodiment discussed above, controlling themotors MG1 and MG2 enables the engine 150 to be driven at any drivingpoint that can output the energy identical with the energy to be outputto the ring gear shaft 126C. The planetary gear 120 and the first motorMG1 in the power output apparatus 110C of the sixth embodiment havesimilar functions to those of the clutch motor 30 in the power outputapparatus 20D of the fourth embodiment, while the second motor MG2 worksin the similar manner to the assist motor 40. The map of FIG. 6 , whichis used to set the target torque Te* and the target revolving speed Ne*of the engine 50 in the torque control of the power output apparatus 20Dof the fourth embodiment, can thus be applicable to set the targettorque Te* and the target revolving speed Ne* of the engine 150 in thetorque control of the power output apparatus 110C of the sixthembodiment.

As discussed previously, all the processes carried out by the poweroutput apparatuses 20 and 20A through 20C of the first through the thirdembodiments and their modification are applicable to the power outputapparatus 110 of the fifth embodiment, by taking into account thebalance on the dynamic collinear line in the nomograms of FIGS. 30 and31. In the same manner, all the processes carried out by the poweroutput apparatus 20D of the fourth embodiment, that is, all theprocesses in the power output apparatuses 20 and 20A through 20C of thefirst through the third embodiments and their modification applied tothe structure where the assist motor 40 is attached to the crankshaft 56of the engine 50, are also applicable to the power output apparatus 110Cof the sixth embodiment, by taking into account the balance on thedynamic collinear line in the nomograms of FIGS. 39 and 40. Namely thepower output apparatus 110C of the sixth embodiment implements the samefunctions and exerts the same effects as those of the power outputapparatuses 20 and 20A through 20C of the first through the thirdembodiments and their modification.

Although the second motor MG2 is interposed between the engine 150 andthe first motor MG1 in the power output apparatus 110C of the sixthembodiment, the engine 150 may be interposed between the first motor MG1and the second motor MG2 as shown by another power output apparatus 110Dof FIG. 41 having a modified structure. In the power output apparatus110C of the sixth embodiment, the power output to the ring gear shaft126C is taken out of the place between the first motor MG1 and thesecond motor MG2 via the power feed gear 128 linked with the ring gear122. As shown by still another power output apparatus 110E of FIG. 42given as another possible modification, however, the power may be takenout of the casing 119, from which a ring gear shaft 126E is extended.

The present invention is not restricted to the above embodiments orapplications, but there may be many modifications, changes, andalterations without departing from the scope or spirit of the maincharacteristics of the present invention. Some examples of possiblemodification are given below.

For example, any one of the power output apparatuses 20 and 20A through20C of the first through the third embodiments may be applied to thevehicle with a four-wheel drive (4WD) as shown in FIG. 43. In thestructure of FIG. 43, the assist motor 40,r which is mechanically linkedwith the drive shaft 22 in the structure of FIG. 1, is separated fromthe drive shaft 22 and independently disposed in a rear-wheel portion ofthe vehicle in order to drive rear driving wheels 27 and 29. One end ofthe drive shaft 22 is linked with a differential gear 24 via a gear 23,so as to drive front driving wheels 26 and 28. The control procedures ofthe first through the third embodiments are also applicable to thestructure of FIG. 43.

FIG. 44 shows another example, in which the power output apparatus 110of the fifth embodiment is applied to the vehicle with a four-wheeldrive (4WD). In the structure of FIG. 44, the second motor MG2, which isattached to the ring gear shaft 126 in the structure of FIG. 27, isseparated from the ring gear shaft 126 and independently disposed in arear-wheel portion of the vehicle in order to drive rear driving wheels117 and 119. The power feed gear 128 linked with the ring gear shaft 126is connected to a differential gear 114 in a front-wheel portion of thevehicle via the chain belt 129 and the power transmission gear 111, soas to drive front driving wheels 116 and 118. The control procedures ofthe fifth embodiment are also applicable to the structure of FIG. 44.The gasoline engine driven by means of gasoline is used as the engine 50or the engine 150 in the above embodiments. The principle of theinvention is, however, applicable to other internal combustion enginesand external combustion engines, such as Diesel engines, turbineengines, and jet engines.

Permanent magnet (PM)-type synchronous motors are used for the clutchmotor 30 and the assist motor 40 in the first through the fourthembodiments and for the first motor MG1 and the second motor MG2 in thefifth and the sixth embodiments. Any other motors which can implementboth the regenerative operation and the power operation, such asvariable reluctance (VR)-type synchronous motors, vernier motors, d.c.motors, induction motors, superconducting motors, and stepping motors,may, however, be used according to the requirements.

The rotary transformer 38 used in the first through the fourthembodiments as means for transmitting the electric power to the clutchmotor 30 may be replaced by a slip ring-brush contact, a slipring-mercury contact, a semiconductor coupling of magnetic energy, orthe like.

Transistor inverters are used for the first and the second drivingcircuits 91 and 92 of the first through the fourth embodiments and forthe fist and the second driving circuits 191 and 192 of the fifth andthe sixth embodiments. Other available examples include IGBT (insulatedgate bipolar mode transistor) inverters, thyristor inverters, voltagePWM (pulse width modulation) inverters, square-wave inverters (voltageinverters and current inverters), and resonance inverters.

The battery 94 in the first through the fourth embodiments or thebattery 194 in the fifth and the sixth embodiments may include Pb cells,NiMH cells, Li cells, or the like cells. A capacitor may be used inplace of the battery 94 or the battery 194. Although the power outputapparatus is mounted on the vehicle in all the above embodiments, it maybe mounted on other transportation means like ships and airplanes aswell as a variety of industrial machines.

It should be clearly understood that the above embodiments discussedabove are only illustrative and not restrictive in any sense. The scopeand spirit of the present invention are limited only by the terms of theappended claims.

We claim:
 1. A power output apparatus for outputting power to a driveshaft, said power output apparatus, comprising:an engine having anoutput shaft; energy adjustment means having a first shaft connectedwith said output shaft of said engine and a second shaft connected withsaid drive shaft, said energy adjustment means adjusting a difference inenergy between power one of input into and output from said first shaftand power one of input into and output from said second shaft byregulating input and output of corresponding electrical energy; a drivemotor, wherein power is transmitted between said drive motor and saiddrive shaft; target power setting means for setting a target poweroutput to said drive shaft; driving state setting means for setting atarget driving state of said engine that outputs energy corresponding tothe target power set by said target power setting means, based on apredetermined condition; and control means for controlling said engine,so as to enable said engine to be driven in the target driving state setby said driving state setting means, and for controlling said energyadjustment means and said drive motor, so as to enable power output fromsaid engine to be subjected to torque conversion and output as thetarget power to said drive shaft.
 2. The power output apparatus inaccordance with claim 1, wherein the predetermined condition in saiddriving state setting means comprises a condition for enhancing anenergy efficiency of said engine that outputs energy corresponding tothe target power.
 3. The power output apparatus in accordance with claim1, wherein the predetermined condition in said driving state settingmeans comprises a condition for enhancing a comprehensive efficiency,which is calculated by multiplying an energy efficiency of said enginethat outputs energy corresponding to the target power by a transmissionefficiency of said energy adjustment means and said drive motor when thepower output from said engine is subjected to torque conversion andoutput to said drive shaft.
 4. The power output apparatus in accordancewith claim 1, wherein the predetermined condition in said driving statesetting means comprises a condition for continuously varying a drivingstate of said engine with a variation in target power.
 5. The poweroutput apparatus in accordance with claim 1, wherein said energyadjustment means comprises a twin-rotor motor comprising a first rotorconnected with said first shaft and a second rotor connected with saidsecond shaft, said second rotor being rotatable relative to said firstrotor, whereby power is transmitted between said first shaft and saidsecond shaft via an electromagnetic coupling of said first rotor withsaid second rotor, said twin-rotor motor inputting and outputtingelectrical energy based on the electromagnetic coupling of said firstrotor with said second rotor and a difference in revolving speed betweensaid first rotor and said second rotor.
 6. A power output apparatus inaccordance with claim 5, wherein said drive motor comprises said secondrotor included in said twin-rotor motor and a stator for rotating saidsecond rotor.
 7. The power output apparatus in accordance with claim 1,wherein said energy adjustment means further comprises:three-shaft-typepower input and output means connected with said first shaft, saidsecond shaft, and a third shaft, said three-shaft-type power input andoutput means for, when powers one of input into and output from any twoshafts among said three different shafts are determined, automaticallysetting a power one of input into and output from a residual shaft basedon the powers thus determined; and a shaft motor connected with saidthird shaft, wherein power is transmitted between said third shaft andsaid shaft motor.
 8. The power output apparatus in accordance with claim1, further comprising driving state detecting means for detecting adriving state of said engine,wherein said control means furthercomprises means for controlling said energy adjustment means, so as toenable said engine to be driven in the target driving state, based onthe driving state of said engine detected by said driving statedetecting means.
 9. The power output apparatus in accordance with claim1, further comprising driving state detecting means for detecting adriving state of said engine,wherein said control means furthercomprises tentative target driving state setting means for, when a statedeviation of the driving state detected by said driving state detectingmeans from the target driving state is out of a predetermined range,selecting a driving state within the predetermined range based on thestate deviation and the predetermined condition and setting the selecteddriving state as a tentative target driving state, the tentative targetdriving state set by said tentative target driving state setting meansbeing used in place of the target driving state for operation control ofsaid engine and control of said energy adjustment means and said drivemotor, until the state deviation enters the predetermined range.
 10. Thepower output apparatus in accordance with claim 9, wherein saidtentative target driving state setting means further comprisespredetermined range setting means for setting the predetermined rangebased on the driving state detected by said driving state detectingmeans.
 11. The power output apparatus in accordance with claim 9,wherein said control means further comprises means for controlling saidenergy adjustment means, so as to enable said engine to be driven in thetarget driving state, based on the driving state detected by saiddriving state detecting means, when the state deviation is within thepredetermined range.
 12. The power output apparatus in accordance withclaim 9, further comprising storage battery means that is charged withelectrical energy taken out of said energy adjustment means, that ischarged with electrical energy taken out of said drive motor, that isdischarged to release electrical energy used in said energy adjustmentmeans, and that is discharged to release electrical energy used in saiddrive motor,wherein said control means further comprises means for, whenthe tentative target driving state is used in place of the targetdriving state for the operation control of said engine and the controlof said energy adjustment means and said drive motor, utilizing theelectrical energy one of stored into and released from said storagebattery means and controlling said drive motor, so as to enable saiddrive motor to one of input and output a specific power one of into andfrom said drive shaft, said specific power corresponding to an energydifference between the target power and the power output from saidengine that is driven in the tentative target driving state.
 13. Thepower output apparatus in accordance with claim 1, wherein said controlmeans further comprises:driving state estimating means for estimating adriving state of said engine when said target power setting means sets adifferent target power; and estimated-condition control means forcontrolling said energy adjustment means and said drive motor based onthe estimated driving state of said engine.
 14. The power outputapparatus in accordance with claim 13, wherein said driving stateestimating means further comprises means for estimating the drivingstate of said engine based on a revolving speed of said output shaft ofsaid engine and a state of said energy adjustment means.
 15. The poweroutput apparatus in accordance with claim 13, wherein saidestimated-condition control means further comprises means forcontrolling said energy adjustment means and said drive motor, so as toenable an estimated power output from said engine corresponding to thedriving state of said engine estimated by said driving state estimatingmeans to be subjected to torque conversion and output as the targetpower to said drive shaft.
 16. The power output apparatus in accordancewith claim 13, further comprising storage battery means that is chargedwith electrical energy taken out of said energy adjustment means, thatis charged with electrical energy taken out of said drive motor, that isdischarged to release electrical energy used in said energy adjustmentmeans, and that is discharged to release electrical energy used in saiddrive motor,wherein said estimated-condition control means furthercomprises means for utilizing the electrical energy one of stored intoand released from said storage battery means and controlling said drivemotor, so as to enable said drive motor to one of input and output aspecific power one of into and from said drive shaft, said specificpower corresponding to an energy difference between the target power andthe estimated power output from said engine corresponding to the drivingstate of said engine estimated by said driving state estimating means.17. A power output apparatus for outputting power to a drive shaft, saidpower output apparatus comprising:an engine having an output shaft;energy adjustment means having a first shaft connected with said outputshaft of said engine and a second shaft connected with said drive shaft,said energy adjustment means adjusting a difference in energy betweenpower one of input into and output from said first shaft and power oneof input into and output from said second shaft by regulating input andoutput of corresponding electrical energy; a drive motor, wherein poweris transmitted between said drive motor and said output shaft of saidengine; target power setting means for setting a target power output tosaid drive shaft; driving state setting means for setting a targetdriving state of said engine that outputs energy corresponding to thetarget power set by said target power setting means, based on apredetermined condition; and control means for controlling said engine,so as to enable said engine to be driven in the target driving state setby said driving state setting means, and for controlling said energyadjustment means and said drive motor, so as to enable power output fromsaid engine to be subjected to torque conversion and output as thetarget power to said drive shaft.
 18. A power output apparatus inaccordance with claim 17, wherein the predetermined condition in saiddriving state setting means comprises a condition for enhancing anenergy efficiency of said engine that outputs energy corresponding tothe target power.
 19. A power output apparatus in accordance with claim17, wherein the predetermined condition in said driving state settingmeans comprises a condition for enhancing a comprehensive efficiency,which is calculated by multiplying an energy efficiency of said enginethat outputs energy corresponding to the target power by a transmissionefficiency of said energy adjustment means and said drive motor when thepower output from said engine is subjected to torque conversion andoutput to said drive shaft.
 20. A power output apparatus in accordancewith claim 17, wherein the predetermined condition in said driving statesetting means comprises a condition for continuously varying a drivingstate of said engine with a variation in target power.
 21. A poweroutput apparatus in accordance with claims-17, 18, 49-r or20,whereinsaidenergy adjustment means comprisesatwin-rotor motor comprising afirst rotor connected with said first shaft and a second rotor connectedwith said second shaft, said second rotor being rotatable relative tosaid first rotor, whereby power is transmitted between said first shaftand said second shaft via an electromagnetic coupling of said firstrotor with said second rotor, said twin-rotor motor inputting andoutputting electrical energy based on the electromagnetic coupling ofsaid first rotor with said second rotor and a difference in revolvingspeed between said first rotor and said second rotor.
 22. The poweroutput apparatus in accordance with claim 21, wherein said drive motorcomprises said first rotor included in said twin-rotor motor and astator for rotating said first rotor.
 23. The power output apparatus inaccordance with claim 17, wherein said energy adjustment means furthercomprises:three-shaft-type power input and output means connected withsaid first shaft, said second shaft, and a third shaft, saidthree-shaft-type power input and output means for, when powers one ofinput into and output from any two shafts among said three differentshafts are determined, automatically setting a power one of input intoand output from a residual shaft based on the powers thus determined;and a shaft motor connected with said third shaft, wherein power istransmitted between said third shaft and said shaft motor.
 24. The poweroutput apparatus in accordance with claim 17, further comprising drivingstate detecting means for detecting a driving state of saidengine,wherein said control means further comprises tentative targetdriving state setting means for, when a state deviation of the drivingstate detected by said driving state detecting means from the targetdriving state is out of a predetermined range, selecting a driving statewithin the predetermined range based on the state deviation and thepredetermined condition and setting the selected driving state as atentative target driving state, the tentative target driving state setby said tentative target driving state setting means being used in placeof the target driving state for operation control of said engine andcontrol of said energy adjustment means and said drive motor, until thestate deviation enters the predetermined range.
 25. The power outputapparatus in accordance with claim 17, wherein said control meansfurther comprises:driving state estimating means for estimating adriving state of said engine when said target power setting means sets adifferent target power; and estimated-condition control means forcontrolling said energy adjustment means and said drive motor based onthe estimated driving state of said engine.
 26. The power outputapparatus in accordance with claim 25, wherein said estimated-conditioncontrol means further comprises means for controlling said energyadjustment means and said drive motor, so as to enable an estimatedpower output from said engine corresponding to the driving state of saidengine estimated by said driving state estimating means to be subjectedto torque conversion and output as the target power to said drive shaft.27. The power output apparatus in accordance with claim 25, furthercomprising storage battery means, that is charged with electrical energytaken out of said energy adjustment means, that is charged withelectrical energy taken out of said drive motor, that is discharged torelease electrical energy used in said energy adjustment means, and thatis discharged to release electrical energy used in said drivemotor,wherein said estimated-condition control means further comprisesmeans for utilizing the electrical energy one of stored into andreleased from said storage battery means and controlling said drivemotor, so as to enable said drive motor to one of input and output aspecific power one of into and from said output shaft of said engine,said specific power corresponding to an energy difference between thetarget power and the estimated power output from said enginecorresponding to the driving state of said engine estimated by saiddriving state estimating means.
 28. A driving system, comprising:anengine having an output shaft; energy adjustment means having a firstshaft connected with said output shaft of said engine and a second shaftconnected with a drive shaft of said driving system, said energyadjustment means adjusting a difference in energy between power one ofinput into and output from said first shaft and power one of input intoand output from said second shaft by regulating input and output ofcorresponding electrical energy; a drive motor, wherein power istransmitted between said drive motor and said drive shaft; target powersetting means for setting a target power output to said drive shaft;driving state setting means for setting a target driving state of saidengine that outputs energy corresponding to the target power set by saidtarget power setting means, based on a first condition for enhancing anenergy efficiency of said engine that outputs energy corresponding tothe target power and a second condition for making a vibration due to anoperation of said engine out of a range of resonance frequency of saiddriving system; and control means for controlling said engine, so as toenable said engine to be driven in the target driving state set by saiddriving state setting means, and for controlling said energy adjustmentmeans and said drive motor, so as to enable power output from saidengine to be subjected to torque conversion and output as the targetpower to said drive shaft.
 29. The driving system in accordance withclaim 28, wherein said energy adjustment means comprises a twin-rotormotor comprising a first rotor connected with said first shaft and asecond rotor connected with said second shaft, said second rotor beingrotatable relative to said first rotor, whereby power is transmittedbetween said first shaft and said second shaft via an electromagneticcoupling of said first rotor with said second rotor, said twin-rotormotor inputting and outputting electrical energy based on theelectromagnetic coupling of said first rotor with said second rotor anda difference in revolving speed between said first rotor and said secondrotor.
 30. The driving system in accordance with claim 29, wherein saiddrive motor comprises said second rotor included in said twin-rotormotor and a stator for rotating said second rotor.
 31. The drivingsystem in accordance with claim 28, wherein said energy adjustment meansfurther comprises:three-shaft-type power input and output meansconnected with said first shaft, said second shaft, and a third shaft,said three-shaft-type power input and output means for, when powers oneof input into and output from any two shafts among said three differentshafts are determined, automatically setting a power one of input intoand output from a residual shaft based on the powers thus determined;and a shaft motor connected with said third shaft, wherein power istransmitted between said third shaft and said shaft motor.
 32. A drivingsystem, comprising:an engine having an output shaft; energy adjustmentmeans having a first shaft connected with said output shaft of saidengine and a second shaft connected with a drive shaft of said drivingsystem, said energy adjustment means adjusting a difference in energybetween power one of input into and output from said first shaft andpower one of input into and output from said second shaft by regulatinginput and output of corresponding electrical energy; a drive motor,wherein power is transmitted between said drive motor and said outputshaft of said engine; target power setting means for setting a targetpower output to said drive shaft; driving state setting means forsetting a target driving state of said engine that outputs energycorresponding to the target power set by said target power settingmeans, based on a first condition for enhancing an energy efficiency ofsaid engine that outputs energy corresponding to the target power and asecond condition for making a vibration due to an operation of saidengine out of a range of resonance frequency of said driving system; andcontrol means for controlling said engine, so as to enable said engineto be driven in the target driving state set by said driving statesetting means, and for controlling said energy adjustment means and saiddrive motor, so as to enable power output from said engine to besubjected to torque conversion and output as the target power to saiddrive shaft.
 33. The driving system in accordance with claim 32, whereinsaid energy adjustment means comprises a twin-rotor motor comprising afirst rotor connected with said first shaft and a second rotor connectedwith said second shaft, said second rotor being rotatable relative tosaid first rotor, whereby power is transmitted between said first shaftand said second shaft via an electromagnetic coupling of said firstrotor with said second rotor, said twin-rotor motor inputting andoutputting electrical energy based on the electromagnetic coupling ofsaid first rotor with said second rotor and a difference in revolvingspeed between said first rotor and said second rotor.
 34. The drivingsystem in accordance with claim 33, wherein said drive motor comprisessaid first rotor included in said twin-rotor motor and a stator forrotating said first rotor.
 35. The driving system in accordance withclaim 32, wherein said energy adjustment means furthercomprises:three-shaft-type power input and output means connected withsaid first shaft, said second shaft, and a third shaft, saidthree-shaft-type power input and output means for, when powers one ofinput into and output from any two shafts among said three differentshafts are determined, automatically setting a power one of input intoand output from a residual shaft based on the powers thus determined;and a shaft motor connected with said third shaft, wherein power istransmitted between said third shaft and said shaft motor.
 36. A methodof controlling a power output apparatus for outputting power to a driveshaft, said method comprising the steps of:(a) providing an enginehaving an output shaft; energy adjustment means having a first shaftconnected with said output shaft of said engine and a second shaftconnected with said drive shaft, said energy adjustment means adjustinga difference in energy between power one of input into and output fromsaid first shaft and power one of input into and output from said secondshaft by regulating input and output of corresponding electrical energy;and a drive motor, wherein power is transmitted between said drive motorand said drive shaft; (b) setting a target power output to said driveshaft; (c) setting a target driving state of said engine that outputsenergy corresponding to the target power set in said step (b), based ona specific condition of selecting a specific driving point that attainsa highest possible efficiency among a plurality of available drivingpoints of said engine that outputs energy corresponding to the targetpower; and (d) controlling said engine, so as to enable said engine tobe driven in the target driving state set in said step (c), and forcontrolling said energy adjustment means and said drive motor, so as toenable power output from said engine to be subjected to torqueconversion and output as the target power to said drive shaft.
 37. Themethod in accordance with claim 36, wherein said step (d) furthercomprises the steps of:(e) detecting a driving state of said engine; (f)when a state deviation of the driving state of said engine detected insaid step (e) from the target driving state is out of a predeterminedrange, selecting a driving state within the predetermined range based onthe state deviation and the specific condition and setting the selecteddriving state as a tentative target driving state; and (g) using thetentative target driving state set in said step (f) in place of thetarget driving state, in order to control said engine, said energyadjustment means, and said drive motor, until the state deviation entersthe predetermined range.
 38. The method in accordance with claim 36,wherein said step (d) further comprises the steps of:(h) when adifferent target power is set, estimating a driving state of said enginebased on a revolving speed of said output shaft of said engine and astate of said energy adjustment means; and (i) controlling said energyadjustment means and said drive motor, so as to enable power output fromsaid engine to be subjected to torque conversion and output to saiddrive shaft, based on the estimated driving state of said engine.
 39. Amethod of controlling a power output apparatus for outputting power to adrive shaft, said method comprising the steps of:(a) providing an enginehaving an output shaft; energy adjustment means having a first shaftconnected with said output shaft of said engine and a second shaftconnected with said drive shaft, said energy adjustment means adjustinga difference in energy between power one of input into and output fromsaid first shaft and power one of input into and output from said secondshaft by regulating input and output of corresponding electrical energy;and a drive motor, wherein power is transmitted between said drive motorand said drive shaft; (b) setting a target power output to said driveshaft; (c) setting a target driving state of said engine that outputsenergy corresponding to the target power set in said step (b), based ona specific condition of selecting a specific driving point that attainsa highest possible efficiency among a plurality of available drivingpoints of said engine that outputs energy corresponding to the targetpower, said comprehensive efficiency being calculated by multiplying anenergy efficiency of said engine by a transmission efficiency of saidenergy adjustment means and said drive motor when the power output fromsaid engine is subject to torque conversion and output to said driveshaft; and (d) controlling said engine, so as to enable said engine tobe driven in the target driving state set in said step (c), and forcontrolling said energy adjustment means and said drive motor, so as toenable power output from said engine to be subjected to torqueconversion and output as the target power to said drive shaft.
 40. Themethod in accordance with claim 39, wherein said step (d) furthercomprises the steps of:(e) detecting a driving state of said engine; (f)when a state deviation of the driving state of said engine detected insaid step (e) from the target driving state is out of a predeterminedrange, selecting a driving state within the predetermined range based onthe state deviation and the specific condition and setting the selecteddriving state as a tentative target driving state; and (g) using thetentative target driving state set in said step (f) in place of thetarget driving state, in order to control said engine, said energyadjustment means, and said drive motor, until the state deviation entersthe predetermined range.
 41. The method in accordance with claim 39,wherein said step (d) further comprises the steps of:(h) when adifferent target power is set, estimating a driving state of said enginebased on a revolving speed of said output shaft of said engine and astate of said energy adjustment means; and (i) controlling said energyadjustment means and said drive motor so as to enable power output fromsaid engine to be subjected to torque conversion and output to saiddrive shaft, based on the estimated driving state of said engine.